M

M

m prefix See milli-.

M prefix See mega-.

Mac- prefix A prefix used to indicate a software product s applicability for the Macintosh computer, as in MacDraw.

Mac n. See Macintosh.

MAC n. Acronym for Media Access Control. In the IEEE 802.x specifications, the lower of two sublayers that make up the ISO/OSI data link layer. The MAC manages access to the physical network, delimits frames, and handles error control. See also IEEE 802.x, LLC.

MacBinary n. A file transfer protocol used to preserve coding for Macintosh-produced files stored in non-Macintosh computers, containing the file s resource fork, data fork, and Finder information block. See also data fork, Finder, resource fork.

Mach n. A variant of the UNIX operating system developed at Carnegie-Mellon University. Mach was designed to support advanced features such as multitasking, multiprocessing, and distributed systems. See also UNIX.

Mach 3.0 n. The microkernel forming the lowest level of the Mac OS X operating system. Mach 3.0 provides basic services such as memory management, thread-handling, virtual memory, and address space management to the operating system kernel.

mach 3 kernel n. See Mach 3.0.

machine address n. See absolute address.

machine code n. The ultimate result of the compilation of assembly language or any high-level language such as C or Pascal: sequences of 1s and 0s that are loaded and executed by a microprocessor. Machine code is the only language computers understand; all other programming languages represent ways of structuring human language so that humans can get computers to perform specific tasks. Also called: machine language. See also compiler (definition 2).

machine cycle n. 1. The time required for the fastest operation (usually a NOP, or no-op, which does nothing) a microprocessor can perform. 2. The steps taken for each machine instruction. These steps are, typically, fetch the instruction, decode it, execute it, and perform any necessary storing.

machine-dependent adj. Of, pertaining to, or being a program or a piece of hardware that is linked to a particular type of computer because it makes use of specific or unique features of the equipment and that cannot easily be used with another computer, if at all. Compare machine-independent.

machine error n. A hardware error. Probably the most common type of machine error involves media, such as an error in reading a hard disk.

machine identification n. A code by which an executing program can determine the identity and characteristics of the computer and other devices with which it is operating.

machine-independent adj. Of, pertaining to, or being a program or piece of hardware that can be used on more than one type of computer with little or no modification. Compare machine-dependent.

machine instruction n. An instruction (action statement) in machine code that can be directly executed by a processor or microprocessor. See also instruction, statement.

machine language n. See machine code.

machine-readable adj. 1. Presented in a form that a computer can interpret and use as input. For example, bar codes that can be scanned and used directly as computer input contain machine-readable information. 2. Coded in the binary form used by computers and stored on a suitable medium such as magnetic tape. See also optical character recognition.

machine translation n. The use of computer software to translate large amounts of text from one natural language into another. Machine translation is usually used by corporations, publishers, and government agencies that need large amounts of documentation, news stories, or business data translated quickly. See also natural-language processing.

Macintosh n. A popular series of personal computers introduced by the Apple Computer Corporation in January 1984. The Macintosh was one of the earliest personal computers to incorporate a graphical user interface and the first to use 3.5-inch floppy disks. It was also the first to use the 32-bit Motorola 68000 microprocessor. Despite its user-friendly features, the Macintosh lost market share to PC-compatible computers during the 1990s, but it still enjoys widespread use in desktop publishing and graphics-related applications. In late 1998, both Apple Computer and Macintosh gained increased visibility with release of the home-oriented iMac computer. See the illustration. Also called: Mac. See also graphical user interface, iMac, PC-compatible.

Macintosh.

Macintosh Application Environment n. A system shell for open RISC-based systems that provides a Macintosh interface within an X Window System window. The Macintosh Application Environment is compatible with both Mac and UNIX and will support all off-the-shelf products for the Macintosh. Acronym: MAE. See also RISC, X Window System.

Macintosh File System n. The early, flat file system used on the Macintosh before the Hierarchical File System was introduced. Acronym: MFS. See also flat file system. Compare Hierarchical File System.

Mac OS n. Short for Macintosh operating system. The name given to the Macintosh operating system, beginning with version 7.5 in September 1994, when Apple started licensing the software to other computer manufacturers. See also Macintosh.

Mac OS X n. The first complete revision of the Macintosh operating system. Mac OS X is BSD 4.4 UNIX-based, uses the Mach 3.0 microkernel, and is built around Apple s open-source Darwin. Mac OS X adds symmetric multiprocessing, multithreading, preemptive multitasking, advanced memory management, and protected memory to the Macintosh. The UNIX foundation of Mac OS X allows greater options for software development, networking, and update and expansion of the operating system. Mac OS X includes a graphical user interface and a command-line interface.

macro n. 1. In applications, a set of keystrokes and instructions recorded and saved under a short key code or macro name. When the key code is typed or the macro name is used, the program carries out the instructions of the macro. Users can create a macro to save time by replacing an often-used, sometimes lengthy, series of strokes with a shorter version. 2. In programming languages, such as C or assembly language, a name that defines a set of instructions that are substituted for the macro name wherever the name appears in a program (a process called macro expansion) when the program is compiled or assembled. Macros are similar to functions in that they can take arguments and in that they are calls to lengthier sets of instructions. Unlike functions, macros are replaced by the actual instructions they represent when the program is prepared for execution; function instructions are copied into a program only once. Compare function (definition 2).

macro assembler n. An assembler that can perform macro substitution and expansion. The programmer can define a macro that consists of several statements and then use the macro name later in the program, thus avoiding having to rewrite the statements. For example, a macro called swap exchanges the values of two variables: After defining swap, the programmer can then insert an instruction such as swap a, b in the assembly language program. While assembling, the assembler replaces the instruction with the statements within the macro that swap the values of the variables a and b.

macrocontent n. The primary text or other content of a Web page. Compare microcontent.

macro expansion n. The act of replacing a macro with its defined equivalent. Also called: macro substitution. See also macro (definition 2), macro assembler, macro processor.

macro instruction n. An instruction used to manage macro definitions. See also macro language.

macro language n. The collection of macro instructions recognized by a given macro processor. See also macro instruction, macro processor.

macro processor n. A program that performs macro expansion. All programs that support macros have some form of macro processor, but macro processors differ from program to program and in the macro language they support. See also macro (definition 2), macro expansion, macro instruction.

macro program n. See keyboard enhancer.

macro recorder n. A program that records and stores keyboard macros. See also macro (definition 1).

macro substitution n. See macro expansion.

macro virus n. A virus that is written in a macro language associated with an application. The macro virus is carried by a document file used with that application and executes when the document is opened.

MacTCP n. A Macintosh extension that allows Macintosh computers to use TCP/IP. See also TCP/IP.

MADCAP n. See multicast address dynamic client allocation protocol.

MAE n. 1. See Macintosh Application Environment. 2. Acronym for Metropolitan Area Exchange. One of the Internet exchange points operated by MCI WorldCom, through which Internet service providers (ISPs) connect in order to exchange data. The two largest MAEs, MAE East (outside Washington, D.C.) and MAE West (near San Jose, California) are major national and international network interconnect points; more than half of all traffic through the Internet travels through one or both of these points. MCI WorldCom also operates smaller, regional MAEs in Chicago, Dallas, Houston, Los Angeles, New York, Paris, and Frankfurt. See also backbone (definition 1), ISP.

Magellan n. A Web directory. Named for the Portuguese explorer, Magellan reviews and rates all Web sites it lists. Published by the McKinley Group, Magellan is now owned by Excite, Inc.

magic date n. A date or dates that in some computer systems resembles a reserved number or flag with a special significance. Examples are the numbers 00 and 99, which have been used in some systems or programs based on two-digit years. Magic dates indicate some special status for example, that a system component or resource should never expire or should never be purged. Because 99 in particular has been used in this way in many systems, dates in the year 1999 had the potential to cause problems in those systems.

magnetic bubble n. A movable magnetic domain in a thin-film substrate. In bubble memory, magnetic bubbles representing bits circulate past circuits that can read and write them. High costs and relatively long access times have relegated magnetic bubbles to specialized applications. See also bubble memory, magnetic domain. Compare core, RAM.

magnetic disk n. A computer disk enclosed in a protective case (hard disk) or jacket (floppy disk) and coated with a magnetic material that enables data to be stored in the form of changes in magnetic polarity (with one polarity representing a binary 1 and the other a 0) on many small sections (magnetic domains) of the disk surface. Magnetic disks should be protected from exposure to sources of magnetism, which can damage or destroy the information they hold. See also disk, floppy disk, hard disk. Compare compact disc, magneto-optic disc.

magnetic domain n. A region of a ferromagnetic material in which the individual atomic or molecular magnetic particles are aligned in the same direction. Also called: ferromagnetic domain.

magnetic field n. The space around a magnetic object in which magnetic force acts. A magnetic field is conceived of as consisting of flux lines that originate at the north magnetic pole and terminate at the south magnetic pole.

magnetic head n. See head.

magnetic-ink character recognition n. A form of character recognition that reads text printed with magnetically charged ink, determining the shapes of characters by sensing the magnetic charge in the ink. Once the shapes have been determined, character recognition methods are used to translate the shapes into computer text. A familiar use of this form of character recognition is to identify bank checks. Acronym: MICR. See also character recognition. Compare optical character recognition.

magnetic oxide n. See ferric oxide.

magnetic storage n. A generic term for non-internal-memory computer data storage involving a magnetic medium, such as disk or tape.

magnetic tape n. See tape (definition 1).

magneto-optical recording n. A type of recording technology used with optical discs in which a laser beam heats a small portion of the magnetic material covering the disc. The heating enables a weak magnetic field to change the orientation of the portion, thus recording onto the disc. This technique can also be used to erase the disc, making the disc rewritable.

magneto-optic disc n. An erasable or semi-erasable storage disc, similar to a CD-ROM disc and of very high capacity, in which a laser beam is used to heat the recording surface to a point at which tiny regions on the surface can be magnetically aligned to store bits of data. See also CD-ROM, magneto-optical recording.

magnitude n. The size of a number, regardless of its sign (+ or ). For example, 16 and 16 have the same magnitude. See also absolute value.

mailbomb¹ n. An excessively large amount of e-mail data (a very large number of messages or one very large message) sent to a user s e-mail address in an attempt to make the user s mailer program crash or to prevent the user from receiving further legitimate messages. See also e-mail¹ (definition 1). Compare letterbomb.

mailbomb² vb. To send a mailbomb to a user. One person might mailbomb a user with a single enormous message; a large number of users might mailbomb an unpopular person by simultaneously sending messages of normal size.

mailbot n. A program that automatically responds to e-mail messages or performs actions based on commands within the messages. A mailing list manager is one example. See also mailing list manager.

mailbox n. A disk storage area assigned to a network user for receipt of e-mail messages. See also e-mail¹ (definition 1).

mail digest n. See digest (definition 2).

mailer-daemon n. A program used to transport e-mail between hosts on a network. See also daemon.

mail filter n. See e-mail filter.

mail header n. A block of text at the top of an e-mail message containing such information as the addresses of the sender and recipients, the date and time sent, the address to which a reply is to be sent, and the subject. The mail header is used by an e-mail client or program. See also e-mail¹ (definition 1).

mailing list n. A list of names and e-mail addresses that are grouped under a single name. When a user places the name of the mailing list in a mail client s To: field, the client sends the message to the machine where the mailing list resides, and that machine automatically sends the message to all the addresses on the list (possibly allowing a moderator to edit it first). See also LISTSERV, mailing list manager, Majordomo, moderator.

mailing list manager n. Software that maintains an Internet or intranet mailing list. The mailing list manager accepts messages posted by subscribers; sends copies of the messages (which may be edited by a moderator) to all the subscribers; and accepts and processes user requests, such as to subscribe or to unsubscribe to the mailing list. The most commonly used mailing list managers are LISTSERV and Majordomo. See also LISTSERV, mailing list, Majordomo, moderator.

mail merge n. A mass-mail facility that takes names, addresses, and sometimes pertinent facts about recipients and merges the information into a form letter or another such basic document.

mail reflector n. A newsgroup that consists simply of the messages posted to a mailing list translated into newsgroup format.

mailto n. A protocol designator used in the HREF of a hyperlink that enables a user to send e-mail to someone. For instance, Anne E. Oldhacker has the e-mail address [e-mail] and an HTML document contains the code <A HREF= mailto:[e-mail] >E-mail Anne!</A>. If a user clicks on the hyperlink E-mail Anne! , the user s e-mail application is launched and the user can send e-mail to her without knowing her actual e-mail address. See also e-mail¹ (definition 1), HTML, hyperlink.

mainboard n. See motherboard.

main body n. The set of statements in a computer program at which execution of the program begins and that invokes the subroutines of the program.

mainframe n. A type of large computer system (in the past often water-cooled), the primary data processing resource for many large businesses and organizations. Some mainframe operating systems and solutions are over 40 years old and have the capacity to store year values only as two digits.

mainframe computer n. A high-level, typically large and expensive computer designed to handle intensive computational tasks. Mainframe computers are characterized by their ability to simultaneously support many users connected to the computer by terminals. The name is derived from main frame, the cabinet originally used to house the processing unit of such computers. See also computer, supercomputer.

main function n. The main body of a program written in a computer language that uses sets of functions to create an entire program. For example, the C language requires each program to contain a function called main, which C uses as the starting point of execution. See also main body.

main loop n. A loop in the main body of a program that performs the principal function of the program over and over until termination is somehow signaled. In event-driven programs, this loop checks for events received from the operating system and handles them appropriately. See also event-driven programming, main body.

main memory n. See primary storage.

main segment n. On the Macintosh, the principal code segment of a program, which must remain loaded throughout the execution of the program.

maintenance n. The process of taking measures to ensure that a hardware, software, or database system is functioning properly and is up to date.

Majordomo n. The name of a popular software program that manages and supports Internet mailing lists. See also mailing list, mailing list manager.

major geographic domain n. A two-character sequence in an Internet domain name address that indicates the country/region in which a host is located. The major geographic domain is the last part of the domain name address, following the subdomain and domain codes; for example, uiuc.edu.us indicates a host at the University of Illinois in the United States, whereas cam.ac.uk indicates a host at the University of Cambridge in the United Kingdom. The code .us, which indicates a domain in the United States, is usually omitted. Also called: country code. See also DNS (definition 1), domain name address.

major key n. See primary key.

Make Changes n. The Macintosh-style permission that gives users the right to make changes to a folder s contents; for example, modifying, renaming, moving, creating, and deleting files. When AppleTalk network integration translates access privileges into permissions, a user who has the Make Changes privilege is given Write and Delete permissions. See also permission.

make-table query n. In Microsoft Office, an action query that moves the resulting data to a new table in either the current database or another database.

male connector n. A type of connector that has pins for insertion into receptacles. Male connector part numbers often include an M (male) or P (plug). For example, a male DB-25 connector might be labeled DB-25M or DB-25P. See the illustration. Compare female connector.

Male connector.

malicious mobile code n. A virus or other destructive program that takes advantage of security weaknesses in wireless transmission systems. Malicious mobile code may affect computers, PDAs, Internet-capable digital phones, and other wireless networking devices.

malware n. Software created and distributed for malicious purposes, such as invading computer systems in the form of viruses, worms, or innocent-seeming plug-ins and extensions that mask other destructive capabilities. Also called: malicious software.

MAME n. Acronym for Multiple Arcade Machine Emulator. MAME is software written in C that emulates the hardware and software of original arcade games, allowing them to run on PCs. See also arcade game, C.

MAN n. Acronym for metropolitan area network. A high-speed network that can carry voice, data, and images at up to 200 Mbps or faster over distances of up to 75 km. Based on the network architecture, the transmission speed can be higher for shorter distances. A MAN, which can include one or more LANs as well as telecommunications equipment such as microwave and satellite relay stations, is smaller than a wide area network but generally operates at a higher speed. Compare LAN, WAN.

managed code n. Code that is executed by the common language runtime environment rather than directly by the operating system. Managed code applications gain common language runtime services such as automatic garbage collection, runtime type checking and security support, and so on. These services provide uniform platform- and language-independent behavior of managed-code applications. See also unmanaged code.

managed service provider n. A business that supplies remote access services to individuals and enterprises. Managed service providers offer remote connections, network management, user support, security, and applications hosting. Acronym: MSP. Compare ISP.

Management and Monitoring Tools n. Software components that include utilities for network management and monitoring, along with services that support client dialing and the updating of client phone books. Also included is the Simple Network Management Protocol (SNMP). See also SNMP.

Management Information Base n. A set of objects that represents various types of information about a device, used by a network management protocol (for example, SNMP) to manage the device. Because different network management services are used for different types of devices and protocols, each service has its own set of objects. Acronym: MIB. See also service, SNMP.

Management Information Services n. See Information Services.

management information system n. A computer-based system for processing and organizing information so as to provide various levels of management within an organization with accurate and timely information needed for supervising activities, tracking progress, making decisions, and isolating and solving problems. Acronym: MIS.

Management Information Systems n. See Information Services.

manager n. Any program that is designed to perform a certain set of housekeeping tasks related to computer operation, such as the maintenance of files. On the Macintosh, Manager (with a capital M) is used in the names of various separate portions of the computer s operating system that handle input, output, and internal functions (for example, File Manager and Memory Manager).

Manchester coding n. A method of encoding data used in communications, such as on some LANs, that combines both data and timing signals in a stream of transmitted bits. See also phase encoding.

mandatory user profile n. A user profile that is not updated when the user logs off. It is downloaded to the user s desktop each time the user logs on, and it is created by an administrator and assigned to one or more users to create consistent or job-specific user profiles. See also local user profile, roaming user profile, user profile.

Mandelbrot set n. See fractal.

man-in-the-middle attack n. A form of attack in which the intruder intercepts messages between parties in a public key exchange. Each party s messages are diverted to the intruder, who may alter them before sending them on. The parties on each end of the exchange remain unaware that their messages are being intercepted and modified. Also called: bucket brigade attack.

man-machine interface n. The set of commands, displays, controls, and hardware devices enabling the human user and the computer system to exchange information. See also user interface.

man pages n. 1. Online documentation for UNIX commands and programs and the UNIX library routines available for use in C programs. These documents, also found in the UNIX Programmer s Manual, can be displayed on a user s terminal or printed using the command man. 2. Short for manual pages. A set of help files included with a Linux distribution. Man pages may come with the Linux distribution and be installed along with the operating system or may be available from online sources.

mantissa n. 1. In calculations that have logarithms, the positive decimal fraction of a common (base-10) logarithm. For example, the common logarithm of 16 is 1.2041; the characteristic, or whole-number portion, of the logarithm is 1 (the logarithm of 10); and the mantissa, or fractional portion, is .2041 (the logarithm of 1.6). See also characteristic, logarithm. 2. In floating-point notation, the portion expressing the significant digits of a number. For example, the floating-point representation of 640,000 is 6.4E+05. The mantissa is 6.4; the exponent (E+05) shows the power of 10 to which 6.4 is raised. Also called: significand. See also floating-point notation.

manual link n. A link that requires you to take action to update your data after the data in the source document changes.

many-to-many relationship n. A complex association between two sets of parameters in which many parameters of each set can relate to many others in the second set. A many-to-many relationship is most commonly used to describe an association between two tables in which one record in either table can relate to many records in the other table.

many-to-one relationship n. 1. A server configuration in which several small servers replicate the abilities of one larger, more powerful server. See also key pair. 2. In reference to asymmetric key encryption, the idea that many individuals in possession of the public key can decrypt the digital signature of one individual in possession of the private key.

map¹ n. Any representation of the structure of an object. For example, a memory map describes the layout of objects in an area of memory, and a symbol map lists the associations between symbol names and memory addresses in a program. See also image map.

map² vb. To translate one value into another. For example, in computer graphics one might map a three-dimensional image onto a sphere. In reference to virtual memory systems, a computer might translate (map) a virtual address into a physical address. See also virtual memory.

MAPI n. Acronym for Messaging Application Programming Interface. The Microsoft interface specification that allows different messaging and workgroup applications (including e-mail, voice mail, and fax) to work through a single client, such as the Exchange client included with Windows 95 and Windows NT. See also application programming interface.

mapped data field n. A field that represents commonly used information, such as First Name. If a data source contains a First Name field or variation, such as FName, the data source field automatically maps to the corresponding mapped data field.

mapped drives n. 1. In the Windows environment, network drives that have been assigned local drive letters and are locally accessible. 2. Under UNIX, disk drives that have been defined to the system and can be made active.

MapPoint n. Business mapping software introduced by Microsoft as an Office-compatible product in 1999. Designed for use by business people, MapPoint consists of a database of United States maps showing detail down to the level of individual streets and demographic data broken out by state, county, zip code, and other regions. See also Office.

margin n. In printing, those portions of a page top, bottom, and sides outside the main body of text.

mark n. 1. In applications and data storage, a symbol or other device used to distinguish one item from others like it. 2. In digital transmission, the state of a communications line (positive or negative) corresponding to a binary 1. In asynchronous serial communications, a mark condition is the continuous transmission of binary 1s to indicate when the line is idle (not carrying information). In asynchronous error checking, setting the parity bit to 1 in each group of transmitted bits is known as mark parity. See also parity. Compare space. 3. In optical sensing, a pencil line, as on a voting form or an IQ test, that can be recognized by an optical reader.

marker n. 1. Part of a data communications signal that enables the communications equipment to recognize the structure of the message. Examples are the start and stop bits that frame a byte in asynchronous serial communications. 2. A symbol that indicates a particular location on a display surface.

Mark I n. 1. An electromechanical calculating machine designed in the late 1930s and early 1940s by Howard Aiken of Harvard University and built by IBM. Also called: Automatic Sequence Controlled Calculator, Harvard Mark I. 2. The first fully electronic stored-program computer, designed and built at Manchester University in England. It successfully executed its first program in June 1948. 3. The first commercial computer, which was based on the Manchester Mark I and released in 1951.

markup n. Comments and tracked changes such as insertions, deletions, and formatting changes that you can view or print.

markup language n. A set of codes in a text file that instructs a computer how to format the file on a printer or video display or how to index and link its contents. Examples of markup languages are Hypertext Markup Language (HTML) and Extensible Markup Language (XML), which are used in Web pages, and Standard Generalized Markup Language (SGML), which is used for typesetting and desktop publishing purposes and in electronic documents. Markup languages of this sort are designed to enable documents and other files to be platform-independent and highly portable between applications. See also HTML, SGML, XML.

marquee n. A nonstandard HTML extension that causes scrolling text to appear as part of a Web page. Currently, marquees are viewable only with Internet Explorer. See also HTML, Internet Explorer, Web page.

marquee component n. A region on a page that displays a horizontally scrolling text message.

mask n. 1. A binary value used to selectively screen out or let through certain bits in a data value. Masking is performed by using a logical operator (AND, OR, XOR, or NOT) to combine the mask and the data value. For example, the mask 00111111, when used with the AND operator, removes (masks off) the two uppermost bits in a data value but does not affect the rest of the value. See the illustration. See also logical operator, mask bit. 2. In television and display technology, a thin perforated sheet of metal or a close-set series of metal strips on the surface of the screen that helps create a clear, sharp image by ensuring that the electron beam for a particular color (red, blue, or green) strikes only the phosphor it is intended to illuminate, while the phosphors for the other colors are shadowed by the mask. Three types of masks are in use: a shadow mask, with round perforations; an aperture grill, with vertical stripes; and a slot mask, with elliptical openings. See also aperture mask, shadow mask, slot mask.

Mask.

maskable interrupt n. A hardware interrupt that can be temporarily disabled (masked) during periods when a program needs the full attention of the microprocessor. See also external interrupt, hardware interrupt, interrupt. Compare nonmaskable interrupt.

mask bit n. A given bit within a binary mask whose function is to screen out or let through the corresponding bit in a data value when the mask is used in an expression with a logical operator. See also mask (definition 1).

masking n. The process of using the mask operation to perform operations on bits, bytes, or words of data. See also mask (definition 1).

mask off vb. To use a mask to remove bits from a byte of data. See also mask (definition 1).

massively parallel processing n. A computer architecture in which each of a large number of processors has its own RAM, which contains a copy of the operating system, a copy of the application code, and its own part of the data, on which that processor works independently of the others. Acronym: MPP. Compare SMP.

massively parallel processor n. A computer designed to perform massively parallel processing.

mass storage n. A generic term for disk, tape, or optical disc storage of computer data, so called for the large masses of data that can be stored in comparison with computer memory capacity. Compare memory.

Master Boot Record n. The first sector of the first hard disk; a physically small but critical element in the startup process on an x86-based computer. When a computer is booted, it processes a series of self-tests and then reads the Master Boot Record, or MBR, into memory. The MBR contains instructions that locate the disk s system (startup) partition, read the contents of the first sector of the system partition into memory, and then carry out the instructions contained in that sector. If the sector represents what is known as a Partition Boot Sector, the instructions found there begin the process of loading and starting the operating system. In other words, the startup process on an x86- based computer is as follows: self-test to Master Boot Record; MBR to system partition and Partition Boot Sector; Partition Boot Sector to operating system; and, finally, a computer ready to go to work. Acronym: MBR. See also Partition Boot Sector.

master file n. In a set of database files, the file containing more or less permanent descriptive information about the principal subjects of the database, summary data, and one or more critical key fields. For example, customers names, account numbers, addresses, and credit terms might be stored in a master file. See also master record. Compare transaction file.

master key n. The server-based component of software or data protection. In some systems, data or applications are stored on a server and must be downloaded to the local machine for use. When a client requests the data, it presents a session key. If the session key supplied matches the master key, the key server sends the requested packet. See also client (definition 3), server (definition 2).

master record n. A record in a master file; typically, the descriptive and summary data related to the item that is the subject of the record. See also master file.

master reseller n. A status assigned by computer equipment manufacturers to dealers and distributors who meet certain qualifications, usually related to the number of pieces the reseller expects to sell.

master/slave arrangement n. A system in which one device, called the master, controls another device, called the slave. For example, a computer can control devices connected to it.

matching n. The process of testing whether two data items are identical or of finding a data item that is identical to a key. See also pattern recognition.

Material Requirements Planning n. An approach to information management in a manufacturing environment that makes use of software to help monitor and control processes related to manufacturing for example, managing schedules and determining when and in what quantities to order materials. Acronym: MRP. Also called: Material Resource Planning. See also Enterprise Resource Planning.

math coprocessor n. See floating-point processor.

mathematical expression n. An expression that uses numeric values, such as integers, fixed-point numbers, and floating-point numbers, and operators, such as addition, subtraction, multiplication, and division. See also expression.

mathematical function n. A function in a program that performs a set of mathematical operations on one or more values or expressions and that returns a numeric value.

mathematical model n. The mathematical assumptions, expressions, and equations that underlie a given program. Mathematical models are used to model real-world physical systems such as planets in orbit around a star or resource production and consumption within a closed system.

MathML n. Acronym for Mathematical Markup Language. An XML application for describing mathematical notation and capturing both its structure and content. The goal of MathML is to enable mathematics to be served, received, and processed on the Web, just as HTML has enabled this functionality for text.

matrix n. An arrangement of rows and columns used for organizing related items, such as numbers, dots, spreadsheet cells, or circuit elements. Matrices are used in mathematics for manipulating rectangular sets of numbers. In computing and computer applications, matrices are used for the similar purpose of arranging sets of data in table form, as in spreadsheets and lookup tables. In hardware, matrices of dots are used in creating characters on the screen as well as in print (as by dot-matrix printers). In electronics, matrices of diodes or transistors are used to create networks of logic circuits for such purposes as encoding, decoding, or converting information. See also grid.

matrix line printer n. See line printer.

MAU n. Acronym for Multistation Access Unit. A hub device in a token-ring network that connects computers in a physical hub-and-spokes arrangement but uses the logical ring required in token ring networks. Also called: MSAU. See also hub, token-ring network.

maximize vb. In a graphical user interface, to cause a window to expand to fill all the space available within a larger window or on the screen. See also enlarge, graphical user interface, Maximize button, window. Compare minimize, reduce.

Maximize button n. In Windows 3.x, Windows 9x, Windows NT, and Windows 2000, a button in the upper right-hand corner of a window that, when clicked, maximizes a window to fill all the space available within a larger window or on the screen. See also graphical user interface, window. Compare Minimize button, zoom box.

Maximum Transmission Unit n. See MTU.

Mb n. See megabit.

MB n. See megabyte.

MBONE or Mbone n. Short for multicast backbone. A small set of Internet sites, each of which can transmit real-time audio and video simultaneously to all the others. MBONE sites are equipped with special software to send and receive packets at high speed using the IP one-to-many multicasting protocol. The MBONE has been used for video conferencing and even for a Rolling Stones concert in 1994. See also RealAudio.

Mbps n. Short for mega bits per second. One million bits per second.

MBR n. See Master Boot Record.

MC n. See megacycle.

MC68000 n. See 68000.

MC68020 n. See 68020.

MC68030 n. See 68030.

MC68040 n. See 68040.

MC68881 n. See 68881.

MCF n. See Meta-Content Format.

MCGA n. Acronym for Multi-Color Graphics Array. An older video adapter included in the IBM PS/2 Models 25 and 30. The MCGA was capable of emulating the CGA (Color/Graphics Adapter) and provided two additional graphics modes: the first mode had 640 horizontal pixels by 480 vertical pixels with 2 colors chosen from a palette of 262,144 colors; the second had 320 horizontal pixels by 200 vertical pixels with 256 colors chosen from a palette of 262,144 colors. See also graphics mode (definition 2).

MCI n. 1. Acronym for Media Control Interface. Part of the Windows application programming interface that enables a program to control multimedia devices. 2. A major long-distance telephone service carrier, originally Microwave Communications, Inc.

m-commerce n. Short for mobile commerce. M- commerce involves the use of personal digital assistants (PDAs), digital phones, and other wireless handheld devices equipped with microbrowsers for the online buying and selling of goods. M-commerce is distinguished from other electronic commerce by the level of portability. Wireless Application Protocol (WAP) standards form the foundation of m-commerce technology, which takes advantage of smart phone capabilities with e-mail, fax, Internet, and phone in one mobile unit. See also microbrowser, Wireless Application Protocol.

MCP n. Acronym for Microsoft Certified Professional. A basic certification from Microsoft that verifies an individual s ability to successfully implement a Microsoft product or technology as part of a solution for an organization. The MCP certification is often used as a building block for acquiring additional certifications in specialized skill areas such as databases, programming languages, and Web development.

MCSA n. Acronym for Microsoft Certified Systems Administrator. A certification from Microsoft that verifies an individual s ability to implement, manage, and troubleshoot existing Microsoft Windows and Windows .NET network and system environments. See also MCP.

MCSD n. Acronym for Microsoft Certified Solution Developer. A certification from Microsoft that verifies an individual s ability to use Microsoft development tools, technologies, and platforms to design and develop business solutions. See also MCP.

MCSE n. Acronym for Microsoft Certified System Engineer. A certification from Microsoft that verifies an individual s ability to analyze business requirements and then design and implement business solutions with Microsoft Windows platforms and server software. See also MCP.

MD2 n. A hashing algorithm that creates a 128-bit hash value used to verify data integrity. MD2 is an earlier, 8-bit version of the more common MD5. See also hashing algorithm.

MD4 n. A hashing algorithm that creates a 128-bit hash value used to verify data integrity. Like the latest version, MD5, MD4 is optimized for 32-bit machines. See also hashing algorithm.

MD5 n. An industry-standard, one-way, 128-bit hashing scheme, developed by MIT Laboratory for Computer Science and RSA Data Security, Inc., and used by various Point-to-Point Protocol (PPP) vendors for encrypted authentication. An extension of MD4, MD5 is slightly slower than the earlier version but offers improved data security. See also hashing algorithm.

MDA n. Acronym for Monochrome Display Adapter. The video adapter introduced with the earliest model of the IBM PC in 1981. MDA was capable of only one video mode: a character mode with 25 lines of 80 characters each, with underlining, blinking, and high-intensity characters. IBM did not use the name Monochrome Display Adapter or the acronym MDA.

MDI n. Acronym for multiple-document interface. A user interface in an application that allows the user to have more than one document open at the same time. See also user interface.

MDIS n. See Metadata Interchange Specification.

mean time between failures n. See MTBF.

mean time to repair n. See MTTR.

mechanical mouse n. A type of mouse in which the motion of a ball on the bottom of the mouse is translated into directional signals. As the user moves the mouse, the ball rolls, turning a pair of wheels mounted at right angles inside the mouse that have conductive markings on their surfaces. Because the markings permit an electric current to flow, a set of conductive brushes that ride on the surface of the conductive wheels can detect these conductive markings. The electronics in the mouse translate these electrical movement signals into mouse-movement information that can be used by the computer. See also mouse, trackball. Compare optical mouse, optomechanical mouse.

mechatronics n. A term derived from the words mechanical and electronics to describe a field of engineering that applies mechanical, electrical, and electronic engineering concepts to product design and manufacture. A relatively new discipline, mechatronics is applicable to products in fields as diverse as medicine, robotics, manufacturing, and consumer electronics.

media n. The physical material, such as paper, disk, and tape, used for storing computer-based information. Media is plural; medium is singular.

Media Access Control n. See MAC.

Media Control Interface n. See MCI (definition 1).

media conversion n. Transferring data from one storage medium to another for example, from disk to tape.

media eraser n. A device that removes or obliterates data from a storage medium on a wholesale basis, usually by writing meaningless data (such as zeros) over it. See also bulk eraser.

media filter n. 1. A device used with local area networks (LANs) as an adapter between two different types of media. For example, an RJ-45 connector might be used between coaxial cable and unshielded twisted pair (UTP) cables. Media filters are similar in function to transceivers. As with many components to LANs, manufacturers often choose different names for similar products, so a LAN expert is needed to decide which media filters are required for a particular LAN. See also coaxial cable, connector (definition 1), LAN, transceiver, UTP. 2. A device added to data networks to filter out electronic noise from the environment. For example, a media filter might be added to an Ethernet network based on coaxial cabling to prevent data loss from interference by nearby electronic equipment. See also coaxial cable, Ethernet (definition 1).

media stream n. A continuous sequence of audio or audio-and-video through a network.

medium¹ adj. Of or relating to the middle part of a range of possible values.

medium² n. A substance in which signals can be transmitted, such as a wire or fiber-optic cable. See media.

medium model n. A memory model of the Intel 80x86 processor family. The medium model allows only 64 kilobytes for data but generally up to 1 megabyte for code. See also memory model.

medium-scale integration n. A concentration of circuit elements in the hundreds on a single chip. Acronym: MSI. See also integrated circuit.

meg n. See megabyte.

mega- prefix One million (10⁶). In computing, which is based on the binary (base-2) numbering system, mega- has a literal value of 1,048,576, which is the power of 2 (2²⁰) closest to one million. Abbreviation: M.

megabit n. Usually 1,048,576 bits (2²⁰); sometimes interpreted as 1 million bits. Abbreviation: Mb, Mbit.

megabyte n. Usually 1,048,576 bytes (2²⁰); sometimes interpreted as 1 million bytes. Abbreviation: MB.

megacycle n. A term for 1 million cycles usually used to mean 1 million cycles per second. Abbreviation: MC. See also megahertz.

megaflops n. See MFLOPS.

megahertz n. A measure of frequency equivalent to 1 million cycles per second. Abbreviation: MHz.

megapel display n. See megapixel display.

megapixel adj. A reference to image resolution of one million pixels or more. The term is used in reference to devices such as digital cameras, scanners, and computer monitors and display adapters.

megapixel display n. A video display capable of displaying at least 1 million pixels. For example, a video display with a screen size of 1024 horizontal pixels and 1024 vertical pixels is a megapixel display. Also called: megapel display.

Melissa n. A macro virus that affects Word files in Microsoft Office 97 and Office 2000 and first appeared in the spring of 1999. Melissa is delivered as an attachment to an e-mail with the subject line An Important Message From <user name>, a message beginning Here is that document you asked for , or both. When the attachment is opened, the virus propagates (if Microsoft Outlook is installed) by sending itself to the first 50 e-mail addresses in the user s Outlook address book. On the infected machine, the virus also changes the registry, infects the Normal.dot Word template (which, in turn, infects new documents), and, in Office 2000, disables the Word macro virus warning. Although the Melissa virus does not destroy data, it can affect e-mail performance through the increased volume of messages. If an infected document is open at a time when the day of the month is the same as the minute value of the current time, the virus inserts the text Twenty-two points, plus triple-word-score, plus fifty points for using all my letters. Game s over. I m outta here at the current location of the cursor. The virus was named after an acquaintance of the hacker who developed it.

meltdown n. 1. The complete collapse of a computer network caused by a higher level of traffic than the network can support. The term refers, by analogy, to the accidental melting down of a nuclear reactor core. 2. Colloquially, the breakdown of a person, usually in a job situation, caused by overwork, stress, or failure.

member n. 1. In object-oriented programming, a variable or routine that is part of a class. See also C++, class. 2. A value that is part of a set data structure. See also set² (definition 1).

membrane keyboard n. A keyboard in which an unbroken plastic or rubber shell (a membrane) covers keys that have little or no travel (movement). Rather than use normal, full-travel keys, membrane keyboards use pressure-sensitive areas that are sometimes, but not always, defined by small bumps under the membrane.

memo field n. A field in a database file that can contain unstructured text.

memo pad n. A note-taking feature offered by many personal digital assistants and other handheld computing devices. Memo pad allows for the entry of short notes via typing or handwriting recognition applications. The notes can be categorized, organized, and edited later.

memory n. A device where information can be stored and retrieved. In the most general sense, memory can refer to external storage such as disk drives or tape drives; in common usage, it refers only to a computer s main memory, the fast semiconductor storage (RAM) directly connected to the processor. See also core, EEPROM, EPROM, flash memory, PROM, RAM, ROM. Compare bubble memory, mass storage.

memory bank n. The physical location on a motherboard where a memory module can be inserted. See also bank (definition 1).

memory board n. A plug-in printed circuit board that contains one or more memory chips. See also memory chip.

memory cache n. See CPU cache.

memory card n. A memory module that is used to extend RAM storage capacity or in place of a hard disk in a portable computer, such as a laptop, notebook, or handheld PC. The module is usually the size of a credit card and can be plugged into a PCMCIA-compliant portable computer. The module can be composed of EPROM, RAM, or ROM chips or flash memory. Also called: RAM card, ROM card. See also EPROM, flash memory, handheld PC, hard disk, memory cartridge, module (definition 2), PCMCIA, RAM, ROM.

memory cartridge n. A plug-in module containing RAM (random access memory) chips that can be used to store data or programs. Memory cartridges are used primarily in portable computers as smaller, lighter (but more expensive) substitutes for disk drives. Memory cartridges typically use either a nonvolatile form of RAM, which does not lose its contents when power is turned off, or battery-backed RAM, which maintains its contents by drawing current from a rechargeable battery within the cartridge. Also called: RAM cartridge. See also memory card, RAM. Compare ROM cartridge.

memory cell n. An electronic circuit that stores one bit of data. See also bit.

memory chip n. An integrated circuit devoted to memory storage. The memory storage can be volatile and hold data temporarily, such as RAM, or nonvolatile and hold data permanently, such as ROM, EPROM, EEPROM, or PROM. See also EEPROM, EPROM, integrated circuit, memory board, nonvolatile memory, PROM, RAM, volatile memory.

memory management n. 1. In operating systems for personal computers, procedures for optimizing the use of RAM (random access memory). These procedures include selectively storing data, monitoring it carefully, and freeing memory when the data is no longer needed. Most current operating systems optimize RAM usage on their own; some older operating systems, such as early versions of MS-DOS, required the use of third-party utilities to optimize RAM usage and necessitated that the user be more knowledgeable about how the operating system and applications used memory. See also memory management unit, RAM. 2. In programming, the process of ensuring that a program releases each chunk of memory when it is no longer needed. In some languages, such as C and C++, the programmer must keep track of memory usage by the program. Java, a newer language, automatically frees any chunk of memory that is not in use. See also C, C++, garbage collection, Java.

memory management program n. 1. A program used to store data and programs in system memory, monitor their use, and reassign the freed space following their execution. 2. A program that uses hard disk space as an extension of the random access memory (RAM).

memory management unit n. The hardware that supports the mapping of virtual memory addresses to physical memory addresses. In some systems, such as those based on the 68020, the memory management unit is separate from the processor. In most modern microcomputers, however, the memory management unit is built into the CPU chip. In some systems, the memory management unit provides interfacing between the microprocessor and memory. This type of memory management unit is typically responsible for address multiplexing and, in the case of DRAMs, the refresh cycle. Acronym: MMU. See also physical address, refresh cycle, virtual address.

memory model n. The approach used to address the code and the data that are used in a computer program. The memory model dictates how much memory can be used in a program for code and how much for data. Most computers with a flat address space support only a single memory model. Computers with a segmented address space usually support multiple memory models. See also compact model, flat address space, large model, medium model, segmented address space, small model, tiny model.

memory module n. A removable circuit board, cartridge, or other carrier that contains one or more RAM memory chips. See also memory card, memory cartridge, RAM.

memory-resident adj. Permanently located in a computer s memory, rather than swapped in and out of memory as needed. See also memory, TSR.

memory scrubbing n. 1. In mainframe computers, the process of a computer reading its own memory during idle periods in order to find and fix errors. 2. The process of examining and correcting errors as data is transferred from memory to the CPU of a computer.

memory size n. The memory capacity of a computer, usually measured in megabytes. See also megabyte, memory.

memory typewriter n. An electric typewriter with internal memory and typically a one-line liquid crystal display for viewing the contents of that memory. Memory typewriters can usually hold one page of text at a time, to which small modifications can be made. Memory typewriters usually do not retain the contents of memory when power is turned off.

MEMS n. Acronym for micro-electromechanical systems. A technology combining computers with extremely tiny mechanical devices. MEMS devices contain microcircuitry on a tiny silicon chip onto which a mechanical device such as a sensor or an actuator is attached. MEMS devices are used in switches, pacemakers, games, GPS tracking, data storage, and for accelerometers in air bags. Because MEMS devices have the potential to be manufactured in large quantities for little cost, many additional MEMS products are being planned or studied.

menu n. A list of options from which a user can make a selection in order to perform a desired action, such as choosing a command or applying a particular format to part of a document. Many application programs, especially those that offer a graphical interface, use menus as a means of providing the user with an easily learned, easy-to-use alternative to memorizing program commands and their appropriate usage.

menu bar n. A rectangular bar displayed in an application program s on-screen window, often at the top, from which menus can be selected by the user. Names of available menus are displayed in the menu bar; choosing one with the keyboard or with a mouse causes the list of options in that menu to be displayed.

menu-driven adj. Using menus to present choices of commands and available options. Menu-driven programs are usually considered friendlier and easier to learn than programs with a command-line interface. Compare command-line interface.

menu item n. A choice on a menu, selectable by either the keyboard or a mouse. In some instances, a menu item that is not available (that is, not appropriate) for a given situation is grayed (dimmed in comparison to the valid menu choices).

Merced n. Former code name for the next-generation 64-bit microprocessor designed by Intel and Hewlett-Packard and released in 2000. Based on the IA-64 architecture, the 64-bit microprocessor contains upwards of 10 million transistors and is used primarily in servers and high-performance workstations. See also IA-64.

Mercury n. A logic/functional programming language that combines the clarity and expressiveness of declarative programming with advanced static analysis and error-detection features.

merge vb. To combine two or more items, such as lists, in an ordered way and without changing the basic structure of either. Compare concatenate.

merged transistor logic n. See integrated injection logic.

merge sort n. A sorting technique that combines several sorted (input) lists into a single sorted (output) list. See also bubble sort, insertion sort, quicksort, sort algorithm.

mesa n. An area of a germanium or silicon wafer that was protected during the etching process and is therefore higher than the surrounding etched areas. See also photolithography.

mesh network n. A communications network having two or more paths to any node.

message n. 1. In communications, a unit of information transmitted electronically from one device to another. A message can contain one or more blocks of text as well as beginning and ending characters, control characters, a software-generated header (destination address, type of message, and other such information), and error-checking or synchronizing information. A message can be routed directly from sender to receiver through a physical link, or it can be passed, either whole or in parts, through a switching system that routes it from one intermediate station to another. See also asynchronous transmission, block (definition 4), control character (definition 1), frame (definition 1), frame (definition 2), header (definition 2), message switching, network, packet (definition 1), packet switching, synchronous transmission. 2. In software, a piece of information passed from the application or operating system to the user to suggest an action, indicate a condition, or inform that an event has occurred. 3. In message-based operating environments, such as Windows, a unit of information passed among running programs, certain devices in the system, and the operating environment itself.

message header n. A sequence of bits or bytes at the beginning of a message that usually provides a timing sequence and specifies such aspects of the message structure as its length, data format, and block identification number. See also header (definition 2).

message of the day n. A daily bulletin for users of a network, multiuser computer, or other shared system. In most cases, users are shown the message of the day when they log into the system. Acronym: MOTD.

Message Passing Interface n. See MPI.

message queue n. An ordered list of messages awaiting transmission, from which they are taken up on a first in, first out (FIFO) basis.

Message Queuing n. A message queuing and routing system for Microsoft Windows that enables distributed applications running at different times to communicate across heterogeneous networks and with computers that may be off line. Message Queuing provides guaranteed message delivery, efficient routing, security, and priority-based messaging. Message Queuing was formerly known as MSMQ.

message reflection n. In object-oriented programming environments, such as Visual C++, OLE, and ActiveX, a function that allows a control to handle its own message. See also ActiveX controls, control (definition 2), OCX, VBX.

Message Security Protocol n. A protocol for Internet messages that is based on the use of encryption and verification to ensure security. It also allows for permissions at the server level for delivery or rejection of e-mail. Acronym: MSP.

message switching n. A technique used on some communications networks in which a message, with appropriate address information, is routed through one or more intermediate switching stations before being sent to its destination. On a typical message-switching network, a central computer receives messages, stores them (usually briefly), determines their destination addresses, and then delivers them. Message switching enables a network both to regulate traffic and to use communications lines efficiently. Compare circuit switching, packet switching.

message transfer agent n. See MTA.

messaging n. The use of computers and data communication equipment to convey messages from one person to another, as by e-mail, voice mail, or fax.

messaging application n. An application that enables users to send messages (such as e-mail or fax) to each other.

Messaging Application Programming Interface n. See MAPI.

messaging client n. An application program that enables its user to send or receive messages (such as e-mail or fax) to and from other users with the help of a remote server.

messaging-oriented middleware n. See MOM.

meta- prefix Literally, a prefix that describes a process or characteristic beyond the normal meaning of the word without the prefix. For example, metaphysics is beyond physics. In computing, meta- is usually attached to a word to indicate that the metaterm describes, defines, or acts upon objects or concepts of the same type as itself. So, for example, metadata is data about data and a metatool is a tool for working on tools.

metacharacter n. A character embedded in a program source or a data stream that conveys information about other characters, rather than itself representing a character. A simple example is the backslash (\) character, which, when used in strings in the C programming language, indicates that the letter following the backslash is part of an escape sequence that enables C to display a nongraphic character. See also escape character.

metacompiler n. A compiler that produces compilers. The UNIX utility yacc (Yet Another Compiler-Compiler) is a metacompiler. If it is given a language specification, yacc produces a compiler for that language. See also compiler (definition 2).

Meta-Content Format n. An open format for describing information about content of a structured body of data such as a Web page, a set of files on a Windows desktop, or a relational database. Meta-Content Format might be used for indexes, data dictionaries, or price lists. Acronym: MCF.

metadata or meta data n. 1. Data about data. For example, the title, subject, author, and size of a file constitute metadata about the file. See also data dictionary, repository. 2. In the Microsoft .NET Framework, information that describes every element managed by the runtime: an assembly, loadable file, type, method, and so on. This can include information required for debugging and garbage collection, as well as security attributes, marshaling data, extended class and member definitions, version binding, and other information required by the runtime.

Metadata Interchange Specification n. A set of specifications dealing with the exchanging, sharing, and managing of metadata. Acronym: MDIS. See also metadata.

metafile n. A file that contains or defines other files. Many operating systems use metafiles to contain directory information about other files on a given storage device.

metaflow n. One of the four stages of the data warehousing process, during which metadata (data about data) is tracked and managed; the business modeling stage. During metaflow, the operational environment is mapped to the data warehouse environment. See also data warehouse (definition 2), downflow, inflow, metadata (definition 1), upflow.

metalanguage n. A language used to describe other languages. Backus-Naur form (BNF) is a metalanguage commonly used to define programming languages. Also called: language-description language. See also Backus-Naur form.

metal-oxide semiconductor n. See MOS.

metal-oxide semiconductor field-effect transistor n. See MOSFET.

metaoperating system n. An operating system under which several other operating systems are active. Also called: supervisor.

metatag or meta tag n. A tag in an HTML or XML document that allows a Web-page creator to include such information as the author s name, keywords identifying content, and descriptive details (for example, non-text objects on the page). The information that is marked with metatags does not appear on the Web page when a user views it in a browser, but it can be viewed in the HTML or XML source. Metatags are included in the head of a document and are often used to assist search engines in indexing the page. See also HTML, source, tag, XML.

method n. In object-oriented programming, a process performed by an object when it receives a message. See also object (definition 2), object-oriented programming.

Metropolitan Area Exchange n. See MAE (definition 2).

metropolitan area network n. See MAN.

MFC n. See Microsoft Foundation Classes.

MFLOPS n. Acronym for million floating-point operations per second. A measure of computing speed. Also called: megaflops.

MFM encoding n. See modified frequency modulation encoding.

MFP n. See multifunction peripheral.

MFS n. See Macintosh File System.

mget n. Short for multiple get. A command in most FTP clients with which a user can request the transfer of several files at once. See also FTP¹ (definition 1).

MHTML n. Acronym for Multipurpose Internet Mail Extension Hypertext Markup Language, or MIME HTML. A standard method for sending an HTML document encapsulated with inline graphics, applets, linked documents, and other items referred to in the HTML document. See also HTML, MIME.

MHz n. See megahertz.

MI n. See multiple inheritance.

MIB n. See Management Information Base.

mickey n. A unit of measure for mouse movement. One mickey is typically equal to 1/200^th of an inch.

MICR n. See magnetic-ink character recognition.

micro- prefix 1. In nonexact measurements, small or compact, as in microprocessor or microcomputer. 2. Metric prefix meaning 10 ⁶ (one millionth).

microbrowser n. An application for mobile phones that allows users to access the Internet to send and receive e-mail and browse the Web. Microbrowsers don t have the full functionality of a Web browser on a PC. For instance, microbrowsers are capable of loading only stripped-down text versions of Web pages. Most microbrowser products are built to utilize the Wireless Application Protocol (WAP) standard. See also Wireless Application Protocol.

microcapsule n. In an electronic paper display, millions of tiny beads filled with dark dye and light pigment that, in response to an electrical charge, change color to create images and text. See also electronic paper.

Micro Channel Architecture n. The design of the bus in IBM PS/2 cosmputers (except Models 25 and 30). The Micro Channel is electrically and physically incompatible with the IBM PC/AT bus. Unlike the PC/AT bus, the Micro Channel functions as either a 16-bit or a 32-bit bus. The Micro Channel also can be driven independently by multiple bus master processors.

microchip n. See integrated circuit.

microcircuit n. A miniaturized electronic circuit etched on a semiconductor chip. A microcircuit is made up of interconnected transistors, resistors, and other components. However, it is fabricated as a unit, rather than as a set of vacuum tubes, discrete transistors, or other elements that have to be wired together. See also integrated circuit.

microcode n. Very low-level code that defines how a processor operates. Microcode is even lower in level than machine code; it specifies what the processor does when it executes a machine-code instruction. See also machine code, microprogramming.

microcomputer n. A computer built around a single-chip microprocessor. Less powerful than minicomputers and mainframes, microcomputers have nevertheless evolved into very powerful machines capable of complex tasks. Technology has progressed so quickly that state-of-the-art microcomputers essentially, in today s terms, a desktop PC are as powerful as mainframe computers of only a few years ago, at a fraction of the cost. See also computer.

microcontent n. Short pieces of text on a Web page that help provide an overview of the page s contents. Microcontent introduces, summarizes, or enhances the macrocontent of a Web page, and includes headings, page titles, ALT text, links, and subheads. Compare macrocontent.

microcontroller n. A special-purpose, single-chip computer designed and built to handle a particular, narrowly defined task. In addition to the central processing unit (CPU), a microcontroller usually contains its own memory, input/output channels (ports), and timers. When part of a larger piece of equipment, such as a car or a home appliance, a microcontroller is an embedded system. See also embedded system.

microdisplay n. A tiny monitor screen that provides a full-size view when magnified. Microdisplays work by magnifying a screen as small as one-tenth of an inch to fill the user s field of vision. Microdisplays may be used with computers, DVD players, or handheld devices, in headsets and viewfinders, or anywhere a full-size monitor is impractical or undesirable.

Microdrive n. A 1-inch disk drive, introduced in 1998 by IBM. The Microdrive is designed for use in handheld computers and special-purpose devices such as digital cameras and cellular telephones.

micro-electromechanical systems n. See MEMS.

microelectronics n. The technology of constructing electronic circuits and devices in very small packages. The most significant advance in microelectronics technology has been the integrated circuit. Circuits that 40 years ago required a roomful of power-hungry vacuum tubes can now be fabricated on a silicon chip smaller than a postage stamp and require only a few milliwatts of power. See also integrated circuit.

microfiche n. A small sheet of film, about 4 by 6 inches, used for recording photographically reduced images, such as document pages, in rows and columns forming a grid pattern. The resulting images are too small to read with the naked eye, and a microfiche reader is required to view the documents. Compare microfilm.

microfilm n. A thin strip of film stored on a roll and used to record sequential data images. As with microfiche, a special device magnifies the images so that they can be read. See also CIM (definition 2), COM (definition 4). Compare microfiche.

microfloppy disk n. A 3.5-inch floppy disk of the type used with the Macintosh and with IBM and compatible microcomputers. A microfloppy disk is a round piece of polyester film coated with ferric oxide and encased in a rigid plastic shell equipped with a sliding metal cover. On the Macintosh, a single-sided microfloppy disk can hold 400 kilobytes (KB); a double-sided (standard) disk can hold 800 KB; and a double-sided high-density disk can hold 1.44 megabytes (MB). On IBM and compatible machines, a microfloppy can hold either 720 KB or 1.44 MB of information. See also floppy disk.

microfluidics n. Technology for control and manipulation of fluids on a microscopic scale using microscopic pumps and valves placed on a chip. Microfluidics devices have implications for a number of medical, pharmaceutical, genomics, and other biotechnology applications.

microform n. The medium, such as microfilm or microfiche, on which a photographically reduced image, called a microimage, is stored. A microimage usually represents text, such as archived documents. See also microfiche, microfilm, micrographics.

micrographics n. The techniques and methods for recording data on microfilm. See also microform.

microimage n. A photographically reduced image, usually stored on microfilm or microfiche, that is too small to be read without magnification. See also microform, micrographics.

microinstruction n. An instruction that is part of the microcode. See also microcode.

microjustification n. See microspace justification.

microkernel n. 1. In programming, the strictly hardware-dependent part of an operating system that is intended to be portable from one type of computer to another. The microkernel provides a hardware-independent interface to the rest of the operating system, so only the microkernel needs to be rewritten to port the operating system to a different platform. See also kernel, operating system. 2. A kernel that has been designed with only the basic features and typically in a modular fashion.

micrologic n. A set of instructions, stored in binary form, or a set of electronic logic circuits that defines and governs the operation within a microprocessor.

microminiature n. An extremely small circuit or other electronic component, especially one that is a refinement of an already miniaturized element.

microphone n. 1. A device that converts sound waves into analog electrical signals. Additional hardware can convert the microphone s output into digital data that a computer can process; for example, to record multimedia documents or analyze the sound signal. 2. A communications program that runs on the Macintosh computer.

microphotonics n. Technology for directing light on a microscopic scale. Microphotonics employs tiny mirrors or photonic crystals to reflect and transmit specific wavelengths of light, which can carry digital signals. Microphotonics technology has implications for optical networks under development for the telecommunications industry. See also MEMS, optical switching.

microprocessor n. A central processing unit (CPU) on a single chip. A modern microprocessor can have several million transistors in an integrated-circuit package that can easily fit into the palm of one s hand. Microprocessors are at the heart of all personal computers. When memory and power are added to a microprocessor, all the pieces, excluding peripherals, required for a computer are present. The most popular lines of microprocessors today are the 680x0 family from Motorola, which powers the Apple Macintosh line, and the 80x86 family from Intel, which is at the core of all IBM PC compatible computers. See also 6502, 65816, 6800, 68000, 68020, 68030, 68040, 80286, 80386DX, 80386SX, 8080, 8086.

microprogramming n. The writing of microcode for a processor. Some systems, chiefly minicomputers and mainframes, allow modification of microcode for an installed processor. See also microcode.

microsecond n. One millionth (10 ⁶) of a second. Abbreviation: ms.

microsite n. 1. A small Web site targeted to a single message or topic and nested within a larger site. Microsites geared to promotional and sales of specific products and services may be integrated into popular Web sites by advertisers. 2. A small Web site with a single focus. Also called: minisite.

Microsoft Access n. See Access.

Microsoft Active Accessibility n. See Active Accessibility.

Microsoft DOS n. See MS-DOS.

Microsoft Excel n. See Excel.

Microsoft Foundation Classes n. A C++ class library developed by Microsoft. The Microsoft Foundation Class library, or MFC, provides the framework and classes that make it easier and faster for programmers to build Windows applications. MFC supports ActiveX and is bundled with several C++ compilers, including Microsoft Visual C++, Borland C++, and Symantec C++. Acronym: MFC. See also ActiveX, C++. Compare Application Foundation Classes.

Microsoft FrontPage n. A program you can use to create and manage Internet and intranet sites without programming; FrontPage is available as part of one of the Microsoft Office suites or as a stand-alone product.

Microsoft intermediate language n. The CPU- independent instruction set into which .NET Framework programs are compiled. It contains instructions for loading, storing, initializing, and calling methods on objects. Combined with metadata and the common type system, Microsoft intermediate language allows for true cross-language integration. Prior to execution, MSIL is converted to machine code. It is not interpreted. Acronym: MSIL.

Microsoft Internet Explorer n. See Internet Explorer.

Microsoft Knowledge Base n. See KB (definition 2).

Microsoft Management Console n. See MMC.

Microsoft MapPoint n. See MapPoint.

Microsoft Money n. See Money.

Microsoft MSN Explorer n. See MSN Explorer.

Microsoft MSN Messenger Service n. See .NET Messenger Service.

Microsoft .NET Messenger Service n. See .NET Messenger Service.

Microsoft Network n. See MSN.

Microsoft Office n. See Office.

Microsoft Operations Manager n. A server and application management solution developed by Microsoft Corporation to deliver event and performance management for the Windows 2000 based environment and .NET Enterprise Server applications. Operations management features include enterprise event log reports from across the corporate network, proactive monitoring and alert messaging, and reporting and trend analysis for problem tracking. Microsoft Operations Manager provides flexibility through sophisticated management rules, which can be customized to meet the needs of individual businesses. Microsoft Operations Manager support for management technology standards permits easy integration with other enterprise management systems.

Microsoft Outlook n. See Outlook.

Microsoft PowerPoint n. See PowerPoint.

Microsoft Project n. A software application developed by Microsoft Corporation to simplify the planning and management of projects. Microsoft Project includes features that help you build and manage projects, set schedules and milestones, and communicate and share ideas with team members.

Microsoft Reader n. A software application developed by Microsoft for downloading electronic books and other publications onto any personal computer, laptop computer, or Pocket PC handheld device. Additional features allow users to bookmark pages, highlight text, write notes, and look up definitions.

Microsoft Tech Ed n. An annual training conference held by Microsoft Corporation to educate engineers and businesses using Microsoft technology. The conference provides attendees with access to information, experts, and training labs on Microsoft s latest technologies.

Microsoft Visual InterDev n. See Visual InterDev.

Microsoft Visual Studio n. See Visual Studio.

Microsoft Visual Studio .NET n. A complete development environment for building on the Microsoft .NET technology. Using Visual Studio .NET, developers can create secure, scalable applications and Web services quickly in the language of their choice, leveraging existing systems and skills.

Microsoft Windows n. See Windows.

Microsoft Windows 2000 n. See Windows 2000.

Microsoft Windows 95 n. See Windows 95.

Microsoft Windows 98 n. See Windows 98.

Microsoft Windows CE n. See Windows CE.

Microsoft Windows Messenger n. See .NET Messenger Service.

Microsoft Windows NT n. See Windows NT.

Microsoft Word n. See Word.

Microsoft XML n. See MSXML.

microspace justification n. The addition of thin spaces between characters within words to fill out a line for justification, instead of relying only on adding space between words. Good microspace justification gives justified text a more polished, professional look; excessive microspace justification causes words to lose visual coherence. Also called: microjustification. See also justify (definition 2), microspacing.

microspacing n. In printing, the process of adjusting character placement by very small increments.

microtransaction n. A business transaction that involves a very small amount of money, typically under about $5. See also millicent technology.

microwave relay n. A communications link that uses point-to-point radio transmissions at frequencies higher than approximately 1 gigahertz (1000 megahertz).

middleware n. 1. Software that sits between two or more types of software and translates information between them. Middleware can cover a broad spectrum of software and generally sits between an application and an operating system, a network operating system, or a database management system. Examples of middleware include CORBA and other object broker programs and network control programs. See also CORBA. 2. Software that provides a common application programming interface (API). Applications written using that API will run in the same computer systems as the middleware. An example of this type of middleware is ODBC, which has a common API for many types of databases. See also application programming interface, ODBC. 3. Software development tools that enable users to create simple programs by selecting existing services and linking them with a scripting language. See also scripting language.

MIDI n. Acronym for Musical Instrument Digital Interface. A serial interface standard that allows for the connection of music synthesizers, musical instruments, and computers. The MIDI standard is based partly on hardware and partly on a description of the way in which music and sound are encoded and communicated between MIDI devices. The information transmitted between MIDI devices is in a form called a MIDI message, which encodes aspects of sound such as pitch and volume as 8-bit bytes of digital information. MIDI devices can be used for creating, recording, and playing back music. Using MIDI, computers, synthesizers, and sequencers can communicate with each other, either keeping time or actually controlling the music created by other connected equipment. See also synthesizer.

MIDL n. Acronym for Microsoft Interface Definition Language. Microsoft implementation and extension of the Interface Definition Language (IDL). See also IDL.

midrange computer n. A medium-size computer. The term is used interchangeably with minicomputer, except midrange computers do not include single-user workstations. See also minicomputer.

migration n. The process of making existing applications and data work on a different computer or operating system.

.mil n. In the Internet s Domain Name System, the top-level domain that identifies addresses operated by U.S. military organizations. The designation .mil appears at the end of the address. See also DNS (definition 1), domain (definition 3). Compare .com, .edu, .gov, .net, .org.

Military Network n. See MILNET.

millennium bug n. See Year 2000 problem.

millennium-compliant adj. See Year 2000-compliant.

millennium computer bug n. See Year 2000 problem.

millennium transition n. See Year 2000 rollover.

milli- prefix Metric prefix meaning 10 ³ (one thousandth). Abbreviation: m.

millicent technology n. A set of protocols for small-scale commercial transactions over the Internet, developed by Digital Equipment Corporation. Millicent technology is intended to handle purchases of items of information at prices less than a cent.

millions of instructions per second n. See MIPS.

millisecond n. One thousandth of a second. Abbreviation: ms or msec.

millivolt n. One thousandth of a volt. Abbreviation: mV.

MILNET n. Short for Military Network. A wide area network that represents the military side of the original ARPANET. MILNET carries nonclassified U.S. military traffic. See also ARPANET. Compare NSFnet.

MIMD n. Acronym for multiple instruction, multiple data stream processing. A category of computer architecture engaged in parallel processing in which central processing units independently fetch instructions and operate on data. See also architecture (definition 1), central processing unit, instruction, parallel processing. Compare SIMD.

MIME or mime n. Acronym for Multipurpose Internet Mail Extensions. A protocol widely used on the Internet that extends the SMTP (Simple Mail Transfer Protocol) to permit data, such as video, sound, and binary files, to be transmitted by Internet e-mail without having to be translated into ASCII format first. This is accomplished by the use of MIME types, which describe the contents of a document. A MIME-compliant application sending a file, such as some e-mail programs, assigns a MIME type to the file. The receiving application, which must also be MIME-compliant, refers to a standardized list of documents that are organized into MIME types and subtypes to interpret the content of the file. For instance, one MIME type is text, and it has a number of subtypes, including plain and html. A MIME type of text/html refers to a file that contains text written in HTML. MIME is part of HTTP, and both Web browsers and HTTP servers use MIME to interpret e-mail files they send and receive. See also HTTP, HTTP server, Simple Mail Transfer Protocol, Web browser. Compare BinHex(definition 1).

mindshare n. The presence and familiarity of a product, service, or company in the minds of users or consumers. Unlike market share, which is the percentage of the market won by a particular product, service, or company, mindshare is a less quantifiable but still important factor in engaging customer attention and generating sales. The term is used frequently by, but is not limited to, the computer industry.

miniaturization n. In the development of integrated circuits, the process of reducing the size and increasing the density of transistors and other elements on a semiconductor chip. In addition to providing the benefits of small size, miniaturization of electronic circuits also lowers power requirements, reduces heat, and shortens delays in the propagation of signals from one circuit element to the next. See also integrated circuit, integration (definition 2).

minicomputer n. A mid-level computer built to perform complex computations while dealing efficiently with a high level of input and output from users connected via terminals. Minicomputers also frequently connect to other minicomputers on a network and distribute processing among all the attached machines. Minicomputers are used heavily in transaction-processing applications and as interfaces between mainframe computer systems and wide area networks. See also computer, mainframe computer, microcomputer, supercomputer, wide area network. Compare midrange computer, workstation (definition 2).

mini-driver architecture n. An architecture in Windows 3.1, Windows 95, Windows 98, Windows NT, and Windows 2000 that uses a relatively small and simple driver, containing any additional instructions needed by a specific hardware device, to interface with the universal driver for that class of devices. See also driver.

minifloppy n. A 5.25-inch floppy disk. See also floppy disk.

minimize vb. In a graphical user interface, to hide a window without shutting down the program responsible for the window. Usually an icon, a button, or a name for the window is placed on the desktop; when the user clicks on the button, icon, or name, the window is restored to its previous size. See also graphical user interface, Minimize button, taskbar, window. Compare maximize.

Minimize button n. In Windows 3.x, Windows 9x, Windows NT, and Windows 2000, a button in the upper right-hand corner of a window that when clicked hides the window. In Windows 3.x and Windows NT 3.5 and earlier, an icon appears on the desktop that represents the window; in Windows 95, Windows NT 4, and later versions, the name of the window appears on the taskbar at the bottom of the desktop screen. When the icon or the name is clicked, the window is restored to its previous size. See also graphical user interface, taskbar, window.

mini-notebook n. A portable computer in a case smaller than that of a standard laptop computer. Most mini-notebook computers have small keyboards, LCD screens built into folding cases, Pentium processors, and built-in hard drives. They are designed to run on standard operating systems, such as Windows 98, rather than on the Windows CE operating system used by the even smaller handheld computers.

miniport driver n. A kernel-mode driver that is specific to a device. A miniport driver is linked to a port driver that provides an interface between the port driver and the operating system. This is typically implemented as a dynamic-link library.

minisite n. See microsite.

minitower n. A vertical floor-standing computer cabinet that is about half the height (13 inches) of a tower case (24 inches). See also tower.

minor key n. See alternate key (definition 1).

MIP mapping n. Short for multum in parvo (Latin, much in little ) mapping. A form of mapping in which the appearance of a bitmapped image is precalculated from a distance and used in a texture mapper. This allows for smoother texture-mapped images calculated in the distance, since pixel conversion may alter colors relative to human perception.

MIPS n. Acronym for millions of instructions per second. A common measure of processor speed. See also central processing unit, MFLOPS.

mirror image n. An image that is an exact duplicate of the original with the exception that one dimension is reversed. For example, a right-pointing arrow and a left-pointing arrow of the same size and shape are mirror images.

mirroring n. 1. In computer graphics, the ability to display a mirror image of a graphic a duplicate rotated or reflected relative to some reference such as an axis of symmetry. See the illustration. 2. In a network, a means of protecting data on a network by duplicating it, in its entirety, on a second disk. Mirroring is one strategy implemented in RAID security. 3. On the Internet, replicating a Web site or an FTP site on another server. A site is often mirrored if it is frequently visited by multiple users. This eases the network traffic to the site, making it easier for users to gain access to the information or files on it. A site may also be mirrored in different geographic locations to facilitate downloading by users in various areas. See also RAID.

Mirroring. (A) twofold symmetry with vertical axis; (B) fourfold symmetry with vertical and horizontal axes; (C) twofold radial symmetry; (D) threefold radial symmetry.

mirror site n. A file server that contains a duplicate set of files to the set on a popular server. Mirror sites exist to spread the distribution burden over more than one server or to eliminate the need to use high-demand international circuits.

MIS n. See IS.

misc. newsgroups n. Usenet newsgroups that are part of the misc. hierarchy and have the prefix misc. These newsgroups cover topics that do not fit into the other standard Usenet hierarchies (comp., news., rec., sci., soc., talk.). See also newsgroup, traditional newsgroup hierarchy, Usenet.

mission critical adj. Pertaining to information, equipment, or other assets of a business or project that are essential to the successful operation of the organization. For example, accounting data and customer records are often considered mission critical information.

misuse detection n. See IDS.

mixed cell reference n. In spreadsheets, a cell reference (the address of a cell needed to solve a formula) in which either the row or the column is relative (automatically changed when the formula is copied or moved to another cell) and the other is absolute (not changed when the formula is copied or moved). See also cell (definition 1).

MMC n. Acronym for Microsoft Management Console. A framework for hosting administrative tools called snap-ins. A console might contain tools, folders or other containers, World Wide Web pages, and other administrative items. These items are displayed in the left pane of the console, called a console tree. A console has one or more windows that can provide views of the console tree. The main MMC window provides commands and tools for authoring consoles. The authoring features of MMC and the console tree itself might be hidden when a console is in User Mode. See also snap-in.

MMDS n. Short for multichannel multipoint distribution service. A fixed wireless service proposed for use as an alternative when DSL or cable modem options are not practical or desirable. The MMDS spectrum was originally used for distance learning and wireless cable video services before attracting interest for fixed broadband wireless services. See also broadband.

MMU n. See memory management unit.

MMX n. Short for Multimedia Extensions. An enhancement to the architecture of Intel Pentium processors that improves the performance of multimedia and communications applications.

mnemonic n. A word, rhyme, or other memory aid used to associate a complex or lengthy set of information with something that is simple and easy to remember. Mnemonics are widely used in computing. Programming languages other than machine language, for example, are known as symbolic languages because they use short mnemonics, such as ADD (for addition) and def (for define) to represent instructions and operations. Similarly, operating systems and applications based on typed commands use mnemonics to represent instructions to the program. MS-DOS, for example, uses dir (for directory) to request a list of files.

MNP10 n. Short for Microcom Networking Protocol, Class 10. An industry-standard communication protocol used for modem connections over analog cellular telephone connections. The most recent version of MNP10 is MNP 10EC (EC stands for Enhanced Cellular). See also communications protocol.

mobile computing n. The process of using a computer while traveling. Mobile computing usually requires a portable computer that is battery powered, rather than a desktop system.

Mobile Explorer n. A modular wireless applications and services platform designed by Microsoft to power Web-enabled wireless telephones. When connected to a wireless network, Mobile Explorer provides secure mobile access to corporate or personal e-mail, corporate networks, and the Internet. It includes a multimode microbrowser, which can display Web content coded in a variety of markup languages used for small, handheld devices, including cHTML, HTML, WAP 1.1, and WML. See also microbrowser.

Mobile Information Server n. A software application developed by Microsoft to allow telecommunications carriers, enterprise customers, and business partners to securely extend Microsoft Exchange Server information, corporate intranet applications, and services to users of wireless handheld computing devices. Microsoft Information Server provides mobile users with access to personal services and data stored on the intranet, such as e-mail, document files, appointment calendars, and contacts.

mobile IP n. Acronym for mobile Internet Protocol. An Internet protocol designed to support host mobility. Mobile IP enables a host to remain connected to the Internet with the same IP address (called the home address) while moving to different locations. Mobile IP tracks a moving host by registering the presence of the host with a foreign agent; the home agent then forwards packets to the remote network. See also IP.

mobile telephone switching office n. Computer that controls wireless phone calls. The mobile telephone switching office controls the operation of wireless cell sites, tracks calls, and transfers signals between wireless networks and traditional wired telephone systems. Acronym: MTSO.

mode n. The operational state of a computer or a program. For example, edit mode is the state in which a program accepts changes to a file. See also address mode, compatibility mode, safe mode, video mode, virtual real mode.

modec n. In telecommunications, a device that generates analog modem signals digitally. The term modec is a combination of the terms modem and codec. See also codec (definition 1), modem (definition 2).

model n. A mathematical or graphical representation of a real-world situation or object for example, a mathematical model of the distribution of matter in the universe, a spreadsheet (numeric) model of business operations, or a graphical model of a molecule. Models can generally be changed or manipulated so that their creators can see how the real version might be affected by modifications or varying conditions. See also modeling, simulation.

modeling n. 1. The use of computers to describe the behavior of a system. Spreadsheet programs, for example, can be used to manipulate financial data representing the health and activity of a company, to develop business plans and projections, or to evaluate the impact of proposed changes on the company s operations and financial status. See also simulation, spreadsheet program. 2. The use of computers to describe physical objects and the spatial relationships among them mathematically. CAD programs, for example, are used to create on-screen representations of such physical objects as tools, office buildings, complex molecules, and automobiles. These models use equations to create lines, curves, and other shapes and to place those shapes accurately in relation to each other and to the two-dimensional or three-dimensional space in which they are drawn. See also CAD, rendering, solid model, surface modeling, three-dimensional model, two-dimensional model, wire-frame model.

modem n. 1. Short for modulator/demodulator. A communications device that converts between digital data from a computer or terminal and analog audio signals that can pass through a standard telephone line. Because the telephone system was designed to handle voice and other audio signals and a computer processes signals as discrete units of digital information, a modem is necessary at both ends of the telephone line to exchange data between computers. At the transmit end, the modem converts from digital to analog audio; at the receiving end, a second modem converts the analog audio back to its original digital form. In order to move a high volume of data, high-speed modems rely on sophisticated methods for loading information onto the audio carrier for example, they may combine frequency shift keying, phase modulation, and amplitude modulation to enable a single change in the carrier s state to represent multiple bits of data. In addition to the basic modulation and demodulation functions, most modems also include firmware that allows them to originate and answer telephone calls. International standards for modems are specified by the International Telecommunications Union, or ITU. Despite their capabilities, modems do require communications software in order to function. See also amplitude modulation, frequency modulation, quadrature amplitude modulation. Compare digital modem. 2. Any communications device that acts as an interface between a computer or terminal and a communications channel. Although such a device may not actually modulate or demodulate analog signals, it may be described as a modem because a modem is perceived by many users to be a black box that connects a computer to a communications line (such as a high-speed network or a cable TV system). See also digital modem.

modem bank n. A collection of modems connected to a server maintained by an ISP or the operator of a BBS or remote-access LAN. Most modem banks are configured to allow a remote user to dial a single phone number that routes calls to an available phone number on the bank. See also BBS (definition 1), ISP, LAN.

modem eliminator n. A device that enables two computers to communicate without modems. See also null modem.

modem port n. A serial port used for connecting an external modem to a personal computer. See also modem (definition 1), serial port.

modem ready n. See MR.

moderated adj. Subjected to review by a moderator, who may remove irrelevant or inflammatory articles or messages before redistributing them through a newsgroup, mailing list, or other messaging system.

moderated discussion n. Communication taking place on a mailing list, newsgroup, or other online forum that is edited by a moderator. When a user submits a message to a moderated discussion, the moderator decides if the message is relevant to the discussion topic. If so, it is forwarded to the discussion group. The content of a moderated discussion is often perceived as more valuable than that of an unmoderated one because the information has been read and approved by a gatekeeper, who has (presumably) filtered out irrelevant submissions. Some moderators also filter submissions for obscene or pornographic material or material that is potentially offensive. See also mailing list, moderator, newsgroup.

moderator n. In some Internet newsgroups and mailing lists, a person through whom all messages are filtered before they are distributed to the members of the newsgroup or list. The moderator discards or edits any messages that are not considered appropriate. See also mailing list, newsgroup.

modified frequency modulation encoding n. An older method of storing data on disks. Modified frequency modulation encoding is based on an earlier technique called frequency modulation encoding but improves on its efficiency by reducing the need for synchronizing information and by basing the magnetic coding of each bit on the status of the previously recorded bit. This method of encoding stores more information on a disk than does frequency modulation encoding. It is not, however, as efficient a space saver as the technique known as run-length limited encoding, or RLL. Abbreviation: MFM encoding. Compare frequency modulation encoding, run-length limited encoding.

modifier key n. A key on the keyboard that, when held down while another key is pressed, changes the meaning of the keystroke. See also Alt key, Command key, Control key, Shift key.

modify structure n. An operator available in some database management systems that permits fields (columns) to be added or deleted without the need to rebuild the entire database.

MO disk n. See magneto-optic disc.

MO disk drive n. See magneto-optic disc.

Modula-2 n. A modular high-level language designed in 1980 by Niklaus Wirth. Derived from Pascal, Modula-2 is noted for its emphasis on modular programming, its early support for data abstraction, and its lack of standard functions and procedures. See also modular programming.

modular design n. An approach to designing hardware or software in which a project is broken into smaller units, or modules, each of which can be developed, tested, and finished independently before being combined with the others in the final product. Each unit is designed to perform a particular task or function and can thus become part of a library of modules that can often be reused in other products having similar requirements. In programming, for example, one module might consist of instructions for moving the cursor in a window on the screen. Because it is deliberately designed as a stand-alone unit that can work with other sections of the program, the same module might be able to perform the same task in another program as well, thus saving time in development and testing.

modular jack n. See phone connector.

modular programming n. An approach to programming in which the program is broken into several independently compiled modules. Each module exports specified elements (such as constants, data types, variables, functions, and procedures); all other elements remain private to the module. Other modules can use only the exported elements. Modules clarify and regularize the interfaces among the major parts of a program. Thus, they facilitate group programming efforts and promote reliable programming practices. Modular programming is a precursor of object-oriented programming. See also module (definition 1), object-oriented programming.

modular software n. A program created from multiple stand-alone software components. Modular components can work together to perform the work for which the larger program is designed while still remaining individually usable and reusable in other programs. Modular software is, in effect, made up of recyclable parts. Because each component is functionally autonomous and self-contained, other components can call on its services without having to know how it works. Thus, a programmer can change or modify the way one component performs its work without adversely affecting other components in the same program. See also component software, integrated software, modular design.

modulate vb. To change some aspect of a signal intentionally, usually for the purpose of transmitting information.

modulation n. 1. The process of changing or regulating the characteristics of a carrier wave vibrating at a certain amplitude (height) and frequency (timing) so that the variations represent meaningful information. 2. In computer communications, the means by which a modem converts digital information sent by a computer to the audio form that it sends over a telephone line.

modulation standards n. Protocols that determine how modems convert digital data into analog signals that can be transmitted over telephone lines. Initially, Bell created modulation standards used in the United States, and the CCITT created international recommendations. The ITU-T (formerly called the CCITT) now makes recommendations generally adopted by modem manufacturers both internationally and in the United States. The ITU-TV series recommendations (such as V.34 and V.90) define data communication over the telephone network. The suffixes -bis and -ter (for example, V.32bis) indicate later versions. See also V.34, V.90.

module n. 1. In programming, a collection of routines and data structures that performs a particular task or implements a particular abstract data type. Modules usually consist of two parts: an interface, which lists the constants, data types, variables, and routines that can be accessed by other modules or routines; and an implementation, which is private (accessible only to the module) and which contains the source code that actually implements the routines in the module. See also abstract data type, information hiding, Modula-2, modular programming. 2. In hardware, a self-contained component that can provide a complete function to a system and can be interchanged with other modules that provide similar functions. See also memory card, SIMM.

modulo n. An arithmetic operation whose result is the remainder of a division operation. For example, 17 modulo 3 = 2 because 17 divided by 3 yields a remainder of 2. Modulo operations are used in programming.

moir n. A visible wavy distortion or flickering in an image that is displayed or printed with an inappropriate resolution. Several parameters affect moir patterns, including the size and resolution of the image, resolution of the output device, and halftone screen angle.

molecular beam epitaxy n. A process used in the fabrication of semiconductor devices, such as integrated circuits. A device employing molecular beam epitaxy creates thin layers of semiconducting material by vaporizing the material and then directing a beam of molecules at the substrate on which the layer is to be formed. This technique allows very precise and very thin layers to be created.

MOM n. Acronym for messaging-oriented middleware. A class of programs that translates data and messages between applications that use one format and communications services (such as NetBIOS and TCP/IP) that expect a different format.

monadic adj. See unary.

Money n. Microsoft s Windows-based financial-management software for individuals, families, and small businesses. Money includes tools for managing bank accounts and investments, budgeting, tax estimating and financial planning, and paying bills.

monitor n. The device on which images generated by the computer s video adapter are displayed. The term monitor usually refers to a video display and its housing. The monitor is attached to the video adapter by a cable. See also CRT.

monitoring software n. A program or set of programs used to oversee computer-based systems and networks for the purpose of tracking usage or identifying, reporting on, and solving problems at the earliest possible stage. Monitoring software is used in a variety of areas ranging from hardware platforms and their components to operating systems, databases, Internet/intranet access, and business applications. Typically, different tools are used to monitor individual system components, though the individual monitors might feed information to a higher-level monitor in order to encompass an entire computing environment.

monitor port n. See display port.

monochrome adj. Of, pertaining to, or being a monitor that displays images in only one color black on white (as on early monochrome Macintosh screens) or amber or green on black (as on early IBM and other monochrome monitors). The term is also applied to a monitor that displays only variable levels of a single color, such as a gray-scale monitor.

monochrome adapter n. A video adapter capable of generating a video signal for one foreground color or sometimes for a range of intensities in a single color, as for a gray-scale monitor.

monochrome display n. 1. A video display capable of rendering only one color. The color displayed depends on the phosphor of the display (often green or amber). 2. A display capable of rendering a range of intensities in only one color, as in a gray-scale monitor.

Monochrome Display Adapter n. See MDA.

monochrome graphics adapter n. See HGC.

monochrome monitor n. See monochrome display.

monographics adapter n. Any video adapter that can display only monochrome text and graphics; any video adapter functionally compatible with the Hercules Graphics Card (HGC). See also HGC.

monospace font n. A font (set of characters in a particular style and size), similar to that used on a typewriter, in which each character occupies the same amount of horizontal space regardless of its width an i, for example, taking as much room as an m. See the illustration. Also called: fixed-width font. See also monospacing. Compare proportional font.

Monospace font. Monospace font vs. proportional font.

monospacing n. A form of print and display spacing in which each character occupies the same amount of horizontal space on the line, regardless of whether the character is wide (such as m) or narrow (such as I). Also called: fixed-pitch spacing, fixed spacing, fixed-width spacing. See also monospace font. Compare proportional spacing.

Monte Carlo method n. A mathematical technique that uses repeated calculations and random numbers to find an approximate solution to a complex problem. The Monte Carlo method, named for its relationship to games of chance played in the casinos at Monte Carlo, Monaco, can be used in situations in which it is possible to calculate the probability of a particular event occurring but not to factor in the complex effects of many other contributing factors.

MOO n. Short for MUD, object-oriented. A type of virtual environment on the Internet, similar to a game-oriented MUD but based on an object-oriented language and generally focused more on programming than on games. See also MUD.

Moore s Law n. A prediction by Intel cofounder Gordon Moore in the early days of the computer revolution regarding the growth of semiconductor technology. Moore predicted that the number of transistors that could be put on a chip would double every year, and it did. Ten years later, Moore predicted that chip capacity would double every two years, and capacity has actually doubled every 18 months since then. The doubling of capacity every 18 months is popularly referred to as a law.

.moov n. A file extension indicating a QuickTime MooV video file for a Macintosh computer. See also MooV.

MooV n. The file format for QuickTime movies that stores synchronized tracks for control, video, audio, and text. See also QuickTime.

morphing n. Short for metamorphosing. A process by which one image is gradually transformed into another, creating the illusion of a metamorphosis occurring in a short time. A common motion picture special-effects technique, morphing is available in many advanced computer animation packages. See also tween.

MOS n. Acronym for metal-oxide semiconductor. An integrated-circuit technology in which field-effect transistors (FETs) are made with an insulating layer of silicon dioxide between a metal gate electrode and a semiconductor channel. MOS designs are widely used both in discrete components and in integrated circuits. MOS integrated circuits have the advantages of high component density, high speed, and low power consumption. MOS devices are easily damaged by static electricity, so before they are inserted in a circuit, they should be kept with their connectors embedded in conducting foam to prevent the buildup of static charges. See also FET, MOSFET.

Mosaic n. The first popular graphical World Wide Web browser. Released on the Internet in early 1993 by the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign, Mosaic is available as freeware and shareware for Windows, Macintosh, and X Window systems. Mosaic is distinguished from other early Web browsers by its ease of use and its addition of inline images to Web documents. Also called: NCSA Mosaic.

MOSFET n. Acronym for metal-oxide semiconductor field-effect transistor. A common type of field-effect transistor in which a layer of silicon dioxide insulates the metal gate from the semiconductor current channel. MOSFETs have extremely high input impedance and therefore require almost no driving power. They are used in many audio applications, including high-gain amplifier circuits. Like all metal-oxide semiconductor (MOS) devices, MOSFETs are easily damaged by static electricity. See the illustration. See also FET, MOS.

MOSFET.

most significant bit n. In a sequence of one or more bytes, the highest-order bit of a binary number, not including the sign bit. Acronym: MSB. See also high-order. Compare least significant bit.

most significant character n. The high-order, or leftmost, character in a string. Acronym: MSC. See also high-order. Compare least significant character.

most significant digit n. In a sequence of one or more digits, the highest-order digit, which is the leftmost digit. In 456.78, 4 is the most significant digit. Acronym: MSD. Compare least significant digit.

MOTD n. See message of the day.

motherboard n. The main circuit board containing the primary components of a computer system. This board contains the processor, main memory, support circuitry, and bus controller and connector. Other boards, including expansion memory and input/output boards, may attach to the motherboard via the bus connector. See also expansion slot. Compare daughterboard.

Motion JPEG n. A standard for storing motion video, proposed by the Joint Photographic Experts Group (JPEG), that uses JPEG image compression for each frame. See also JPEG (definition 1). Compare MPEG (definition 1).

motion path n. The path that a specified object or text will follow as part of an animation sequence for a slide.

mount vb. To make a physical disk or tape accessible to a computer s file system. The term is most commonly used to describe accessing disks in Macintosh and UNIX-based computers.

mount n. In NFS, a folder or file retrieved from elsewhere on the network and accessed locally. See also NFS.

MOUS n. Acronym for Microsoft Office User Specialist. A certification from Microsoft that verifies an individual s skills with the Microsoft Office desktop programs. See also MCP.

mouse n. A common pointing device. The basic features of a mouse are a flat-bottomed casing designed to be gripped by one hand, one or more buttons on the top, a multidirectional detection device (usually a ball) on the bottom, and a cable connecting the mouse to the computer. By moving the mouse on a surface (such as a desk top), the user typically controls an on-screen cursor. A mouse is a relative pointing device because there are no defined limits to the mouse s movement and because its placement on a surface does not map directly to a specific screen location. To select items or choose commands on the screen, the user presses one of the mouse s buttons, producing a mouse click. See the illustration. See also bus mouse, mechanical mouse, optical mouse, optomechanical mouse, relative pointing device, serial mouse. Compare trackball.

Mouse. Two types of mouse: for the Macintosh (left) and for the PC (right).

MouseKeys n. A feature in Windows that allows a user to use the numeric keyboard to move the mouse pointer. MouseKeys is primarily intended for people who may have physical limitations that make it difficult to move a conventional mouse. See also mouse.

mouse pad n. A surface on which a mouse can be moved, typically a rectangular rubber pad covered with fabric, providing more traction than a wooden or glass desktop or tabletop. See also mouse.

mouse pointer n. An on-screen element whose location changes as the user moves the mouse. Depending on the location of the mouse pointer and the operation of the program with which it is working, the area of the screen where the mouse pointer appears serves as the target for an action when the user presses one of the mouse buttons. See also block cursor, cursor (definition 3).

mouse port n. 1. In many PC-compatible computers, a dedicated connector where a mouse or other pointing device plugs into the computer. If a mouse port is not available, a serial port can be used to connect the mouse to the computer. See the illustration. See also connector, mouse, pointing device, serial port. 2. In a Macintosh, the Apple Desktop Bus port. See also Apple Desktop Bus.

Mouse port.

mouse scaling n. See mouse sensitivity.

mouse sensitivity n. The relationship of mouse movement to screen cursor movement. A more sensitive mouse signals to the computer more mouse moves per inch of physical mouse movement than does a less sensitive mouse. Increasing the sensitivity of the program or mouse driver can result in smaller cursor moves for a given mouse move, making it easier for the user to position the cursor precisely. High sensitivity is good for exacting work, such as CAD/CAM and graphic art; low sensitivity is good for tasks in which getting around the screen quickly is important and for applications such as Web browsers, word processors, and spreadsheets, in which the cursor is used mostly to select buttons or text. Also called: mouse scaling, mouse tracking.

mouse tracking n. See mouse sensitivity.

mouse trails n. The creation of a shadowlike trail following the mouse pointer on screen in order to make it easier to see. Mouse trails are useful for laptops and notebooks, particularly ones with passive matrix displays or older models with monochrome screens. The relatively low resolution and contrast of these screens made it easy to lose sight of a small mouse pointer. See also mouse pointer, submarining.

mousetrapping n. A practice employed by some Web sites in which the back and exit buttons of a visitor s Web browser are disabled and attempts to leave the site are redirected to other pages on the site or to other sites against the visitor s will. Mousetrapping is most often associated with adult-oriented Web sites. Compare page-jacking.

.mov n. A filename extension for a movie file in Apple s QuickTime format. See also QuickTime.

move n. A command or an instruction to transfer information from one location to another. Depending on the operation involved, a move can affect data in a computer s memory or it can affect text or a graphical image in a data file. In programming, for example, a move instruction might transfer a single value from one memory location to another. In applications, on the other hand, a move command might relocate a paragraph of text or all or part of a graphic from one place in a document to another. Unlike a copy procedure, which duplicates information, a move indicates that information either is or can be deleted from its original location. Compare copy.

.movie n. See .mov.

Moving Picture Experts Group n. See MPEG (definition 1).

Mozilla n. 1. A nickname for the Netscape Navigator (later, Netscape Communicator) Web browser, coined by the Netscape Corporation. See also Mosaic, Netscape Navigator. 2. Since 1998, when the Communicator source code was released for free, for use by any interested parties, the name Mozilla has been extended as a generic reference to any Web browser based on Navigator source code.

mozilla.org n. The name of the group charged by the Netscape Corporation to act as a clearinghouse for Mozilla-related matters, such as questions, changes to code, bug reporting, forums, and so on.

MP3 n. Acronym for MPEG Audio Layer-3. A digital audio coding scheme used in distributing recorded music over the Internet. MP3 shrinks the size of an audio file by a factor of 10 to 12 without seriously degrading the quality (CD-recording level) of the sound. MP3 files are given the file extension .mp3. Although MP3 is part of the MPEG family, it is audio-only and is not the same as the now-defunct MPEG-3 standard. See also MPEG-3.

MP3 encoder n. See encoder.

MPC n. See Multimedia PC.

.mpeg n. The file extension that identifies video and sound files compressed in the MPEG format specified by the Moving Pictures Experts Group. See also MPEG.

MPEG n. 1. Acronym for Moving Picture Experts Group. A set of standards for audio and video compression established by the Joint ISO/IEC Technical Committee on Information Technology. The MPEG standard has different types that have been designed to work in different situations. Compare Motion JPEG. 2. A video/audio file in the MPEG format. Such files generally have the extension .mpg. See also JPEG. Compare Motion JPEG.

MPEG-1 n. The original MPEG standard for storing and retrieving video and audio information, designed for CD-ROM technology. MPEG-1 defines a medium bandwidth of up to 1.5 Mbps, two audio channels, and noninterlaced video. See also MPEG (definition 1). Compare MPEG-2, MPEG-3, MPEG-4.

MPEG-2 n. An extension of the MPEG-1 standard designed for broadcast television, including HDTV. MPEG-2 defines a higher bandwidth of up to 40 Mbps, five audio channels, a wider range of frame sizes, and interlaced video. See also HDTV, MPEG (definition 1). Compare MPEG-1, MPEG-3, MPEG-4.

MPEG-3 n. Initially an MPEG standard designed for HDTV (high-definition television), but it was found that MPEG-2 could be used instead. Therefore, this standard no longer exists. See also HDTV, MPEG (definition 1). Compare MP3, MPEG-1, MPEG-2, MPEG-4.

MPEG-4 n. A standard currently under development designed for videophones and multimedia applications. MPEG-4 provides a lower bandwidth of up to 64 Kbps. See also MPEG (definition 1). Compare MPEG-1, MPEG-2, MPEG-3.

.mpg n. See .mpeg.

MPI n. Acronym for Message Passing Interface. A specification for message passing on workstation clusters and massively parallel processing (MPP) architectures. MPI was designed as a proposed standard by the MPI Forum, a committee of vendors and users.

MPLS n. Acronym for Multiprotocol Label Switching. A standards-based technique used to manage and optimize traffic flow for large-scale networks. In an MPLS network, incoming packets are assigned a label by a label edge router (LER). Label switch routers (LSRs) use these labels to forward the packets through the network along a label switch path (LSP). Each LSR removes the existing label and assigns a new one. MPLS combines the advantages of bridges (Layer 2 switching, which is used in ATM and frame relay) and routers (Layer 3 switching, which is used in IP). MPLS serves to create faster and more scalable networks to facilitate quality of service, class of service, and the use of VPNs.

MP/M n. Acronym for Multitasking Program for Microcomputers. A multitasking, multiuser version of the CP/M operating system. See also CP/M.

MPOA n. Acronym for Multi-Protocol Over ATM. A specification established by the ATM Forum (an industry group of Asynchronous Transfer Mode users and vendors) to integrate ATM into existing Ethernet, token ring, and TCP/IP networks. See also ATM (definition 1).

MPP n. See massively parallel processing, massively parallel processor.

MPPP n. See Multilink Point-to-Point Protocol.

MPR II n. A standard for limiting magnetic and electric field emissions from video monitors, including VLF radiation. MPR II is a voluntary standard developed by the Swedish Board for Measurement and Testing in 1987 and updated in 1990. See also VLF radiation.

mput n. In many FTP clients, the command that instructs the local client to transmit multiple files to the remote server.

MR n. Acronym for modem ready. A light on the front panel of a modem indicating that the modem is ready.

MRP n. See Material Requirements Planning.

ms n. See millisecond.

MSAA n. See Active Accessibility. Short for Microsoft Active Accessibility.

MSAU n. See MAU.

MS Audion. n. The code name, or working name, of Windows Media Audio, before the technology was released by Microsoft. See also Windows Media Audio.

MSB n. See most significant bit.

MSC n. See most significant character.

MSD n. See most significant digit.

MSDN n. Acronym for the Microsoft Developer Network. An online, print, and CD-DVD resource for developers that features content and programs focused on development trends and Microsoft technologies. Some features of MSDN include technical articles and reference material; information on upcoming conferences and events; developer support through peer-to-peer interaction, information sharing, and direct interaction with Microsoft; and software subscription programs.

MS-DOS n. Short for Microsoft Disk Operating System. A single-tasking, single-user operating system with a command-line interface, released in 1981, for IBM PCs and compatibles. MS-DOS, like other operating systems, oversees operations such as disk input and output, video support, keyboard control, and many internal functions related to program execution and file maintenance.

MS-DOS mode n. A shell in which the MS-DOS environment is emulated in 32-bit systems such as Windows 95. See also MS-DOS, shell¹.

MS-DOS shell n. A shell environment based on a command-line prompt that allows a user to interact with MS-DOS or an MS-DOS-emulating operating system.

MSDOS.SYS n. One of two hidden system files installed on an MS-DOS startup disk. MSDOS.SYS, called IBMDOS.SYS in IBM releases of MS-DOS, contains the software that makes up the heart (kernel) of the operating system. See also IO.SYS.

msec n. See millisecond.

MSI n. See medium-scale integration.

MSIL n. See Microsoft intermediate language.

MSN n. Acronym for Microsoft Network. An online service and Internet portal, launched with the introduction of Windows 95 in August 1995.

MSN Explorer n. Microsoft software that integrates the functionality of Internet Explorer, Windows Media Player, Hotmail, MSN Messenger, MSN Communities, Music Central, and other MSN content and services. See also MSN.

MSN Messenger Service n. See .NET Messenger Service.

MSP n. See Message Security Protocol, managed service provider.

MS-Windows n. See Windows.

MSXML n. Acronym for Microsoft XML. A Java-based XML parser from Microsoft that provides support for World Wide Web Consortium (W3C) standards for XML documents and applications.

MTA n. Acronym for message transfer agent. An application process, as described in the X.400 message-handling system, responsible for delivering e-mail messages. After receiving a message, an MTA stores it temporarily and either delivers it or forwards it to another MTA. During this process, the MTA can change the message headers. See also X series.

MTBF n. Acronym for mean time between failures. The average time interval, usually expressed in thousands or tens of thousands of hours (sometimes called power-on hours or POH), that will elapse before a hardware component fails and requires service.

MTTR n. Acronym for mean time to repair. The average time interval, usually expressed in hours, that it takes to repair a failed component.

MTU n. Acronym for Maximum Transmission Unit. The largest packet of data that can be transmitted on a network. MTU size varies, depending on the network 576 bytes on X.25 networks, for example, 1500 bytes on Ethernet, and 17,914 bytes on 16 Mbps Token Ring. Responsibility for determining the size of the MTU lies with the link layer of the network. When packets are transmitted across networks, the path MTU, or PMTU, represents the smallest packet size (the one that all networks can transmit without breaking up the packet) among the networks involved.

MUD n. Acronym for multiuser dungeon. A virtual environment on the Internet in which multiple users simultaneously participate in a role-playing game generally a medieval fantasy, hence the dungeon and interact with each other in real time. Also called: multiuser simulation environment.

MUD, object-oriented n. See MOO.

multiband phone n. Wireless phone that operates on two or more broadcast frequencies.

multiboot n. 1. Startup capability of some operating systems, such as Windows NT, OS/2, UNIX, and some Power Macs, that allows users to choose which of two or more installed operating systems for example, Windows NT or UNIX they want to use for the current session. See also boot. 2. A computer configuration that runs two or more operating systems. See also dual boot, startup.

Multibus n. A computer expansion bus designed by Intel Corporation that is used extensively by designers of high-performance workstations. A high-bandwidth bus (capable of extremely fast data transmission), Multibus also allows multiple bus masters. See also bus.

multicast address dynamic client allocation protocol n. An extension to the DHCP protocol standard used to support dynamic assignment and configuration of IP multicast addresses on TCP/IP-based networks. Acronym: MADCAP.

multicast backbone n. See MBONE.

multicasting n. The process of sending a message simultaneously to more than one destination on a network. Compare anycasting..

multichannel multipoint distribution service n. See MMDS.

Multi-Color Graphics Array n. See MCGA.

multi-element adj. Consisting of multiple data elements that all have the same format for storing the same kind of information. The data elements may be simple variables, as in an array of integer variables, or they may be more complicated data structures, as in an array of employee records each of which contains fields for an employee s name, Social Security number, pay rate, and so on.

multifile sorting n. The process of sorting a body of data that resides in more than one file.

MultiFinder n. A version of the Macintosh Finder that provides support for multitasking. The primary use of MultiFinder is to allow multiple applications to be simultaneously resident in memory. A single mouse click switches between applications, and information from one application can be copied to another. If the active application allows true multitasking, background tasks can be processed. See also Finder.

multifunction board n. A computer add-in board that provides more than one function. Multifunction boards for personal computers frequently offer additional memory, serial/parallel ports, and a clock/calendar.

multifunction peripheral n. A multipurpose device that combines printing with faxing, scanning (color or black and white), and copying (color or black and white) in a single unit. Multifunction peripherals are especially popular with the SOHO (small office, home office) market, where cost-effectiveness and space limitations can be significant considerations. Acronym: MFP. Also called: multifunction printer.

multifunction printer n. See multifunction peripheral.

multihoming n. 1. In Mac OS X, an automatic network selection feature that allows one computer to maintain multiple network addresses. Multihoming may be used with a computer that is used from multiple locations, such as home and office, or to create special connection settings, such as separate systems for communication inside and outside of an intranet. 2. The use of multiple addresses and/or multiple interfaces for a single node. A multihomed host has either multiple network interfaces connected to two or more networks, or a single network interface that has been assigned multiple IP addresses. Multihoming can be used to provide redundancy to achieve quality of service.

multilayer adj. 1. In board design, of or pertaining to a printed circuit board consisting of two or more layers of board material. Each separate layer has its own metallic tracings to provide electrical connections between various electronic components and to provide connections to the other layers. The layers are laminated together to produce a single circuit board to which the components, such as integrated circuits, resistors, and capacitors, are attached. Multilayer design allows many more discrete paths between components than single-layer boards do. 2. In computer-aided design (CAD), of or pertaining to drawings, such as electronic circuits, that are built up using multiple layers, each with a different level of detail or a different object, so that distinct parts of the drawing can easily be manipulated, overlaid, or peeled off.

multilayer switch n. A network switch that uses information from more than one ISO/OSI layer (Layer 2, Layer 3, Layer 4, and/or Layer 7) to forward traffic. See also ISO/OSI reference model, switch (definition 4).

Multilink Point-to-Point Protocol n. An Internet protocol that allows computers to establish multiple physical links to combine their bandwidths. This technology creates a virtual link with more capacity than a single physical link. Acronym: MPPP. See also PPP.

multimedia n. The combination of sound, graphics, animation, and video. In the world of computers, multimedia is a subset of hypermedia, which combines the aforementioned elements with hypertext. See also hypermedia, hypertext.

Multimedia Extensions n. See MMX.

Multimedia PC n. Software and hardware standards set forth by the Multimedia PC Marketing Council, which sets minimum standards for a PC s sound, video, and CD-ROM playing capabilities. Acronym: MPC.

Multimedia Personal Computer n. See Multimedia PC.

multimode phone n. Wireless phone that operates on both analog and digital networks. A multimode phone may be dual-mode (analog and one digital network) or tri-mode (analog and two digital networks).

multinode computer n. A computer that uses multiple processors to share in the computation of a complex task. See also central processing unit, parallel processing.

multipart forms n. Computer printer paper arranged in sets with carbon paper between the sheets (or with a chemical coating that emulates carbon on the back of each sheet except the last) to produce copies of output from impact printers. Multipart forms are designated by the number of copies in a set, such as two-part, three-part, and so on.

multipartite virus n. A type of virus that combines characteristics and techniques of both boot sector and file viruses. Multipartite viruses first infect either system sectors or files and then spread quickly to infect the entire system. Because of their multiple capabilities, multipartite viruses are difficult to remove from an infected system. Also called: bimodal virus, bipartite virus. See also boot.

multipass sort n. A sorting operation that, usually because of the sorting algorithm being used, requires two or more passes through the data before completion. See also bubble sort, insertion sort, Shell sort, sort algorithm.

multiple-document interface n. See MDI.

multiple inheritance n. A feature of some object-oriented programming languages that allows a new class to be derived from several existing classes. Multiple inheritance both extends and combines existing types. Acronym: MI. See also class, inherit, type.

multiple instruction, multiple data streams n. See MIMD.

multiple master font n. An advanced font creation and management classification developed by Adobe. A multiple master font contains two or more sets of font outlines or master designs that determine the dynamic range of each design axis in a typeface. Multiple master fonts include one or more design axes weight, width, style, and optical size that allow the user to create thousands of variations on a single typeface.

multiple-pass printing n. A form of dot-matrix printing in which the print head makes more than one pass across the page for each printed line, printing each line a second time exactly on top of the first pass. Multiple-pass printing can be used with dot-matrix printers to darken the print and smooth out errors in alignment. On better printers, a second pass might occur after the paper is moved up slightly, so that the dots in the characters overlap to create a crisper, darker image.

multiple recipients n. 1. The capability of sending e-mail to more than one user at a time by listing more than one e-mail address on a line. Delimiters such as commas or semicolons are used to separate the e-mail addresses. See also e-mail (definition 1), mailing list. 2. The subscribers on a mailing list. A message sent to the list is addressed to the multiple recipients of the list.

multiple regression n. A statistical technique that seeks to describe the behavior of a so-called dependent variable in terms of the observed behavior of numerous other, independent variables thought to affect it. For each independent variable, a regression analysis can determine the correlation coefficient of the independent variable that is, the degree to which variations in the independent variable cause changes in the dependent variable. See also dependent variable.

multiple-user system n. See multiuser system.

multiplexer n. A device for funneling several different streams of data over a common communications line. Multiplexers are used either to attach many communications lines to a smaller number of communications ports or to attach a large number of communications ports to a smaller number of communications lines. Acronym: MUX.

multiplexer channel n. One of the inputs to a multiplexer. See also multiplexer.

multiplexing n. A technique used in communications and input/output operations for transmitting a number of separate signals simultaneously over a single channel or line. To maintain the integrity of each signal on the channel, multiplexing can separate the signals by time, space, or frequency. The device used to combine the signals is a multiplexer. See also FDM, space-division multiplexing, time-division multiplexing.

multiplicand n. In arithmetic, the number that is multiplied by another number (the multiplier). In mathematics, the multiplicand and the multiplier are interchangeable, depending on how the problem is stated, because the result is the same if the two are reversed for example, 2 x 3 and 3 x 2. In arithmetic performed by computers, however, the multiplicand is different from the multiplier because computer multiplication is usually performed as addition. Therefore, 2 x 3 means add 2 three times, whereas 3 x 2 means add 3 two times. See also factor. Compare multiplier (definition 1).

multiplier n. 1. In arithmetic, the number that indicates how many times another number (the multiplicand) is multiplied. See also factor. Compare multiplicand. 2. In computing, an electronic device independent of the central processing unit (CPU) that performs multiplication by adding the multiplicand according to the value of the digits in the multiplier.

multipoint configuration n. A communications link in which multiple stations are connected sequentially to the same communications line. Typically, the communications line is controlled by a primary station, such as a computer, and the stations attached to the line are secondary. See the illustration.

Multipoint configuration.

multiport repeater n. See active hub.

multiprocessing n. A mode of operation in which two or more connected and roughly equal processing units each carry out one or more processes (programs or sets of instructions) in tandem. In multiprocessing, each processing unit works on a different set of instructions or on different parts of the same process. The objective is increased speed or computing power, the same as in parallel processing and in the use of special units called coprocessors. Compare coprocessor, parallel processing.

multiprogramming n. A form of processing in which a computer holds more than one program in memory and works on them in round-robin fashion that is, by sharing out the processor s time so that each program receives some attention some of the time. This way of working is in contrast to using the processor to run one program at a time.

Multiprotocol Label Switching n. See MPLS.

Multi-Protocol Over ATM n. See MPOA.

Multipurpose Internet Mail Extensions n. See MIME.

Multipurpose Internet Mail Extensions HTML n. See MHTML.

multiscan monitor n. A computer monitor capable of adapting to different video frequencies to accommodate multiple screen resolutions and to support different video adapters and graphics display methods.

Multistation Access Unit n. See MAU.

multisystem network n. A communications network in which two or more host computers can be accessed by network users.

multitasking n. A form of processing supported by most current operating systems in which a computer works on multiple tasks roughly, separate pieces of work seemingly at the same time by parceling out the processor s time among the different tasks. Multitasking can be either cooperative or preemptive. In the former, the operating system relies on the task to voluntarily cede control to another task; in the latter, the operating system decides which task receives priority. See also background¹, context switching, cooperative multitasking, foreground¹, time slice.

multithreaded application n. A program capable of running more than one program thread simultaneously. See also multithreading (definition 1), thread (definition 1).

multithreading n. 1. The running of several processes in rapid sequence (multitasking) within a single program. See also thread (definition 1). 2. In data manipulation, a technique in which nodes in a tree data structure contain pointers to higher nodes to make traversal of the structure more efficient. See also thread (definition 2).

multi-tier n. See three-tier.

multiuser n. See multiuser system.

multiuser dungeon n. See MUD.

multiuser simulation environment n. See MUD.

multiuser system n. Any computer system that can be used by more than one person. Although a microcomputer shared by several people can be considered a multiuser system, the term is generally reserved for machines that can be accessed simultaneously by several people through communications facilities or via network terminals. Compare single-user computer.

multum in parvo mapping n. See MIP mapping.

MUMPS n. Acronym for Mass(achusetts) Utility Multi Programming System. An advanced, high-level programming language and integrated database developed in 1966 at Massachusetts General Hospital and used widely by health care businesses. A unique feature of MUMPS is its ability to store both data and program fragments in its database.

munging n. See address munging.

MUSE n. See MUD. Short for multiuser simulation environment..

.museum n. One of seven new top-level domain names approved in 2000 by the Internet Corporation for Assigned Names and Numbers (ICANN), .museum is meant for use by museum Web sites.

Musical Instrument Digital Interface n. See MIDI.

mutual exclusion n. A programming technique that ensures that only one program or routine at a time can access some resource, such as a memory location, an I/O port, or a file, often through the use of semaphores, which are flags used in programs to coordinate the activities of more than one program or routine. See also semaphore.

MUX n. See multiplexer.

My Briefcase n. A Windows 9x utility, helpful for workers away from the office, that manages the updating of modified files once the remote user s computer is connected back on the office network.

Mylar n. A polyester film product created by DuPont, often used as the base for magnetically coated storage media (disks and tape) and for carbon ribbons used with impact printers.

Mylar ribbon n. See carbon ribbon.

MYOB n. Acronym for Mind your own business. An expression used in e-mail and newsgroups.

my two cents n. An expression used informally in newsgroup articles and, less frequently, e-mail messages or mailing lists, to indicate that the message is the writer s contribution to an ongoing discussion. Also called: $0.02. See also mailing list, newsgroup.