Z

Z

.z n. The file extension identifying a UNIX file compressed using the gzip or compact utility. See also gzip.

.Z n. The file extension for UNIX files that have been compressed using the compress utility. See also compress.

Z39.50 standard n. A specification for a query language based on SQL (structured query language). It is used by WAIS, among other Internet services, to search for files through the use of keywords and is widely used for remote access to library catalogs. See also structured query language, WAIS.

Z80 n. An 8-bit microprocessor from Zilog, a company founded by former Intel engineers. The Z80 has a 16-bit address bus, yielding a 64-kilobyte addressable memory space, and an 8-bit data bus. A descendant of the Intel 8080, it was the favored processor in the days of the CP/M operating system. One of the most popular computers of the early 1980s, the Radio Shack TRS-80, was based on this chip. See also CP/M.

zap vb. 1. To erase permanently. For example, to zap a file means to remove it without hope of retrieval. 2. To damage a device, usually by discharging static electricity through it.

z-axis n. The third axis in a three-dimensional coordinate system, used in computer graphics to represent depth. See also Cartesian coordinates, coordinate system.

ZB n. See zettabyte.

zepto- prefix A metric prefix meaning 10 ²¹ (one sextillionth in the American system).

zero¹ n. The arithmetic symbol (0) representing no magnitude.

zero² vb. To fill or replace with zeros (for example, to zero a specified portion of memory, a field, or some other limited structure).

zero divide n. A division operation in which the divisor is zero. Division by zero is mathematically undefined, is not allowed in a program, and is considered a bug.

zero flag n. A flag (bit) in a microprocessor that is set (turned on), typically in a flag register, when the result of an operation is zero. See also flag (definition 1).

zero-insertion-force socket n. See ZIF socket.

zero-length string n. A string that contains no characters. You can use a zero-length string to indicate that you know there s no value for a field. You enter a zero-length string by typing two double quotation marks with no space between them ("").

zero out vb. To set a variable value or a series of bits to zero.

zero suppression n. The elimination of leading (nonsignificant) zeros in a number. For example, zero suppression would truncate 000123.456 to 123.456. See also significant digits.

zero wait state n. The condition of random access memory (RAM) that is fast enough to respond to the processor without requiring wait states. See also wait state.

zetta- prefix A metric prefix meaning 10²¹ (one sextillion in the American system).

zettabyte n. A unit of measure equal to 2⁷⁰ bytes, or one sextillion (10²¹) bytes. When calculated as a multiple of 1000 exabytes (the next highest unit of measure), a zettabyte is 1,000,000,000,000,000,000,000 bytes; when calculated as 1024 exabytes, a zettabyte is 1,180,591,620,717,411,303,424 bytes. The prefix (zetta-) is meant to sound like the Greek letter zeta.Abbreviation: ZB.

z-fold paper n. See fanfold paper.

ZIF socket n. Short for zero-insertion-force socket. A kind of socket for integrated circuits that can be opened with a lever or screw, allowing the chip to be placed in the socket without the application of pressure. The lever or screw of the socket is then closed, causing the socket contacts to grip the chip s pins. ZIF sockets facilitate frequent insertion and removal of chips, but they take up more space and are more expensive than conventional sockets.

zinc-air battery n. Non rechargeable battery that is relatively inexpensive, offers extended battery life, and contains none of the harsh chemicals or metals found in conventional nickel metal cadmium (NiCad), nickel metal hydride (NiMH), or lithium ion (Li-ion) batteries.

.zip n. A file extension that identifies a compressed archive file encoded in ZIP format, as by PKZIP. See also compressed file, PKZIP.

Zip drive n. A disk drive developed by Iomega that uses 3.5-inch removable disks (Zip disks) capable of storing 100 megabytes of data. See the illustration. See also disk drive.

Zip drive.

Zmodem n. An enhancement of the Xmodem file transfer protocol that handles larger data transfers with less error. Zmodem includes a feature called checkpoint restart, which resumes transmission at the point of interruption, rather than at the beginning, if the communications link is broken during data transfer. See also Xmodem.

zombie n. A computer that has become the unwilling host of a DDoS (distributed denial of services) attack program and that is controlled by remote signals from the attacker. To create a zombie, a hacker utilizes security vulnerabilities to crack a Web, mail, news, or application server and plant hidden DDoS tools such as Trinoo and Tribal Flood Network. Later, at a signal from the attacker, the server becomes a zombie that will participate in a coordinated attack on other servers. See also DDoS, hacker.

zone n. 1. On a LAN (local area network), a subgroup of users within a larger group of interconnected networks. 2. In Macintosh programming, a portion of memory that is allocated and reallocated by the memory manager facility as memory is requested and released by applications and by other parts of the operating system. See also heap (definition 1).

zone header n. On the Apple Macintosh, a header at the beginning of a block of memory that contains information needed by the memory management facility in order to use that memory block effectively. See also header (definition 2).

zone transfer n. The process whereby a secondary DNS server obtains information about a zone or domain from the primary server. See also zone (definition 1).

.zoo n. The file extension that identifies compressed archive files created with the zoo file compression utility. See also zoo210.

zoo210 n. Version 2.1 of zoo, a program for creating compressed archive files (whose names have the extension .zoo). The algorithm for zoo210 is based on that of LHARC. Implementations of zoo210 are available for UNIX and Intel systems. See also archive file, LHARC.

zoom vb. To enlarge a selected portion of a graphical image or document to fill a window or the screen. Zooming is a feature of many programs, including drawing, word processing, and spreadsheet programs, that allows the user to select a small part of the screen, zoom it, and make changes to the enlarged portion at a finer level of detail. See also window.

zoom box n. A control in the upper right corner of the frame of a window on the Macintosh screen. When the user clicks on the zoom box, the window toggles between the maximum size and the size the user has set for it by dragging. See also window. Compare Maximize button.

zoomed video port n. See ZV port.

zoo virus n. A virus that is kept in an isolated environment for the benefit of anti-virus research and training. Zoo viruses are not found outside the labs of anti-virus companies.

Zope n. An open source application server for publishing objects on the Internet. Zope provides tools to integrate data and content from multiple sources into complete Web applications and can be used in conjunction with XML-RPC to form a system for remotely scriptable Web objects. Zope runs on UNIX, Windows NT and later, and most other major operating systems. See also XML-RPC.

z-order n. 1. The order in which objects are drawn on top of one another onscreen to simulate depth (the third dimension) in conjunction with the x and y (height and width) coordinates. 2. The visual layering of windows or controls on a form along the z-axis (depth). The z-order determines which controls are in front of other controls. Each window or control has a unique position in the z-order.

Zulu time n. Slang for Greenwich Mean Time.

ZV port n. Short for zoomed video port. Port available on many portable computers as an inexpensive multimedia alternative to traditional video input. The ZV port allows data to flow uninterrupted from source to destination without need for buffering. Zoomed video was adopted by the Personal Computer Memory Card International Association (PCMCIA) to enable high transfer rates for portable computers, connected video cameras, and other multi media devices.