Among the early electronic computers were the Atanasoff-Berry Computer (ABC), ENIAC (Electronic Numerical Integrator and Computer), and Colossus.
Today's computer professional needs to be a technician, a scholar, and a diplomat.
A computer bus is a group of electrical conductors (usually wires) running parallel to each other. These conductors can be copper traces on a circuit board or wires in a cable. Usually, they are found in multiples of eight (8, 16, 32, 64, and so on).
The purpose of the computer bus is to provide a common path to transmit information, in the form of code, to all parts of the computer.
Digital, as it is used in this book, refers to the binary digits 0 (off) and 1 (on).
Serial communication sends each piece of information one bit at a time on one wire, and parallel communication sends as many bits of information at a time as there are parallel wires.
Binary code language is computer language. The language is called binary because it is based on two states or numbers (0 and 1) represented by a switch condition being set either on or off.
Computers use the binary system for communication, based on eight bits (or one byte) of information being transmitted at one time. To support this, a standard code called ASCII (American Standard Code for Information Interchange) was developed as the basis for computer communication. Basic ASCII consisted of 128 binary codes that represented the English alphabet, punctuation, and certain control characters.
A bit is the smallest unit of information that is recognized by a microcomputer. It is similar to a light bulb in that it can exist only in two states—it is either on or it is off.
A byte is a group of eight bits. To represent one character of information requires one byte.
This binary number represents the number 9.
1s and 0s represent voltage to a computer: the absence of voltage represents a 0 bit, and the presence of voltage represents a 1 bit.
Computer buses are usually found in multiples of 8 wires or traces.
The three stages of computing are input, processing, and output.
The central processing unit (CPU) is the heart and brain of the computer. This one component or "chip" does all the number crunching and data management.
The CPU and the chip set process information inside a computer.
A chip set is a group of computer chips or ICs (integrated circuits) that, when working in harmony, manage and control the computer system.
The mouse, keyboard, microphone, and scanner are examples of input devices.
A scanner is an input device.
The printer, monitor, and speakers are examples of output devices.
Many devices can handle both input and output functions. These devices are called I/O devices.
The floppy disk drive, hard disk drive, modem, and network interface card are examples of I/O devices.
Binary code is the language of the computer.
The external data bus is the primary bus for handling the flow of data. All devices that process data are connected to the external data bus.
An integrated circuit is an electronic device consisting of many miniature transistors and other circuit elements (resistors and capacitors, for instance).
The timing for all activities within a computer is set by the computer's clock (but not the one that keeps time). Each pulse of voltage produced by the clock is called a "clock cycle."
Many improvements were made to the Pentium chip that made it superior to the 486, including:
The 80386DX was a true 32-bit processor with a 32-bit external data bus, 32-bit registers, and a 32-bit address bus (enabling 4 GB of memory to be accessed). The 80386SX was similar to the DX except that it had a 16-bit external data bus and a 24-bit address bus (it could address only 16 MB of memory).
Some Apple Macintoshes use the Motorola 68040 chip.
A microprocessor is an integrated circuit that contains a complete CPU on a single chip.
In computer code language the number 1 means on and the number 0 means off.
Clock speed, a main selling point for today's PC computer, is the system clock rate, measured in megahertz (MHz). One MHz equals one million cycles per second. Clock speed is the number of times per second that a computer can process an instruction.
The CPU accesses memory through an additional bus called the address bus. The number of conductors in the address bus determines the maximum amount of memory that can be used by the CPU.
Examples of chip packages are DIPP, PGA, PLCC, and PQFP.
The LIF (low-insertion-force) and ZIF (zero-insertion-force) sockets are the two basic CPU sockets. The Pentium II and later Intel processors use Slot 1 sockets.
Consider upgrading the CPU and motherboard to a newer CPU and matching motherboard.
Spikes and surges are brief, but often catastrophic, increases in the voltage source (very high voltage for a very short time). These can be caused by the power source (the local power company), but most often are caused by lightning strikes. A spike (or transient) is a very short over-voltage condition measured in nanoseconds, while a surge is measured in milliseconds. A sag is a brief decrease of voltage at the source.
AT style with two plugs—P8 and P9, and the ATX style with a single connector.
The Molex, a 5-volt connector, is used for hard disk drives, and the mini 3.3-volt is used for floppy disk drives and similar devices.
The UPS (uninterruptible power supply) buys the user some time in which to save data and properly shut down a system, in the event that a power outage has occurred. And the UPS conditions the line in the event of a spike or surge.
A brownout is a decrease in the voltage in the power supply. A blackout is a total power failure.
That the UPS offers enough time to power the computer until all data can be saved and the computer can be properly shut down.
No, surge suppressors offer limited protection, and it decreases with age. Also, nothing can totally protect against a nearby full-force lightning strike.
To protect against spikes from lightning, unplug your computer from the wall outlet.
The black (ground) wires must be installed next to each other.
The Molex connector is the most common connector, and is used primarily for devices that need both 12-volt and 5-volt power, such as older floppy disk drives, hard disk drives, and CD-ROM drives.
The mini connector is used primarily on 3.5-inch floppy drives. Most systems provide a mini connector.
Take the old one with you and match its physical size, as well as the power ratings and number of connectors, to the new one.
Mini connectors are primarily used for 3.5-inch floppy disk drives.
The 5-volt output is used to power devices that manage data only, and the 12-volt output is used to power devices that have moving parts, such as drives and fans.
The motherboard is the primary card in the computer. It defines the limits for CPU type, speed, memory, and expandability.
A motherboard comes with several chips soldered in place. They constitute the chip set and are designed to work with the CPU. These chips are highly complex and coordinated ICs that help the CPU manage and control the computer's system. Included in the chip set are the clock generator, bus controller, system timer, interrupt controller, DMA controller, CMOS, and keyboard controller.
EMI stands for electromagnetic interference. EMI is the same thing as radio frequency interference (RFI), but EMI is a newer term. EMI is considered to be any radio frequency that is emitted from an electrical or electronic device that is harmful to the surrounding equipment or that interferes with the operation of another electrical or electronic device.
ROM chips are used extensively to program the operation of computers, but ROM plays a limited role in the PC; it holds the BIOS information used to describe the system configuration and the instructions for performing the POST routine.
The first type of ROM chip is called the core chip and includes hardware that is common, necessary, and unchanging. The second type of ROM chip is hardware that is common, necessary, and changeable; these chips are called updatable chips. The third type of chip includes any chip other than the first two types of chips.
The CMOS chips are updatable, and that makes them special. They do not store programs like other ROM chips do; they store only data that is used by BIOS for the programs needed to communicate with changeable hardware. The CMOS chip also maintains date-and-time information when the computer is powered off.
The purpose of the first POST (power-on self test) is to check the most basic components. Because the video integrity has not been confirmed, any errors that occur in this phase are indicated by a series of beeps. A technician can use the beep codes to interpret any problems that occur before the video is confirmed.
A device driver is a program that acts as an interface between the operating system and the control circuits that operate the device.
Typically, the CMOS contains at least the following information: floppy and hard disk drive types, CPU and memory size, date and time, and serial- and parallel-port information.
Every time a computer is turned on or reset, the entire system is reset. From this on or reset state, it begins to carry out software instructions from its BIOS program. The first set of instructions it initiates is a special program (stored on a ROM chip) called the power-on self test (POST). The POST sends out standardized commands that check every device (in more technical terms, it runs an internal self-diagnostic routine).
Hexadecimal shorthand (hex, for short) is a numbering system used by designers and programmers to simplify the representation of numbers and notations. Known as "base-16 mathematics," it is a complete numbering system based on 16 instead of 10. Just as in the base-10 system, you can add, subtract, or do trigonometry with hex.
Conventional memory is the first 640 KB of memory in a computer. The first 1 MB of memory was divided into two sections: 384 KB of RAM (designated upper memory) for running the computer (BIOS, video RAM, and ROM), and 640 KB for applications (designated).
Expanded memory is memory that conforms to the EMS specification, developed by Lotus, Intel, and Microsoft. It requires a special device driver. EMS is accessed through 64-KB blocks of the upper memory.
Extended memory is any memory beyond the first 1 MB.
HMA is the first 64 KB of extended memory on machines with 80286 or higher processors.
Shadow RAM rewrites (or shadows) the contents of the ROM BIOS and/or video BIOS into extended RAM memory (between the 640-KB boundary and 1 MB). This allows systems to operate faster when application software calls for any BIOS routines.
ROM is read-only memory and cannot be changed. It is usually used for BIOS or other data that cannot be lost if the power is off.
RAM is random access memory and is constantly changing. It is used as the main working memory for a computer. RAM memory is lost if the power is turned off.
Because a 486 computer has a 32-bit external data bus, it requires four 30-pin SIMMs per bank. Remember, a 30-pin SIMM is only one byte (8-bits) wide; therefore, you need to divide the width of the bus by the width of the SIMM—that is, 32 (the width of data bus) divided by 8 (the number of bits per SIMM module).
Some caches immediately send all data directly to RAM, even if it means hitting a wait state. This is called write-through cache. Some caches store the data for a time and send it to RAM later. This is called a write-back cache.
DRAM (dynamic random access memory) is volatile memory that works only when the computer has power. This is the "scratch pad" that the CPU uses to manipulate data.
The time required to complete a memory read or to write actions is known as the access speed of the memory chip. This time is usually very small and is measured in nanoseconds (one-billionth of a second—abbreviated as ns). The faster the chip, the smaller the access-speed number.
A SIPP (single inline pin package) is a printed circuit board with individual DRAM chips mounted on it. SIMMs (single inline memory modules) are the new generation of memory chips. They are similar to SIPPs, with one exception—SIMMs have no pins, as such. 30-pin SIMMs have 30 contacts along the edge.
To cache means to set something aside, or to store nearby, for anticipated use. Mass storage (disk drives) is much slower than RAM, and RAM is much slower than the CPU. Caching increases the speed of the system by creating special storage areas in high-speed memory.
Refreshing means that the information must be updated constantly or it will be lost. SRAM does not require that extra step that can slow things down (nothing can access the memory during a refresh). Because SRAM is faster, the circuitry required is more expensive.
The IDE (Integrated Drive Electronics) drive was introduced in the early 1990s. The IDE quickly became the standard for general-purpose computers. The purpose of the IDE specification was to increase data throughput, support non-hard disk drive storage devices, increase the capacity of hard drives beyond the 528-MB barrier, and to allow connection of up to four devices instead of only two.
Two drives can be connected to one IDE connector.
The best method of determining the number of drives available on a computer is to run the CMOS setup program. Originally, the CMOS would only allow for two drives. Later versions allow up to four drives.
Three things to check when a floppy disk drive fails are the floppy disk itself (not the drive), the CMOS setup, and the drive controller/power supply cables.
To ensure long life from a floppy disk drive, keep it clean.
Floppy disk drive controller cards also include some or all of the following: hard disk drive controllers, serial ports, parallel ports, and game ports. If the new card contains any ports that duplicate ports already present elsewhere on the computer (on the motherboard, for instance), a potential conflict exists.
The only difference between a 5.25-inch and a 3.5-inch drive (other than physical size) is that a 5.25-inch drive has a slot connector and a 3.5-inch drive has a pin connector for engaging and spinning the disk.
All floppy disk drives are connected to the motherboard (external data bus) by a 34-conductor ribbon cable. This cable has a seven-wire twist in lines 10 through 16. This ensures that when two floppy disk drives are attached, the drive-select and motor-enable signals on those wires can be inverted to "select" which drive becomes the active target. The other wires carry data and ground signals.
The connector end of the cable, with the twist, always goes toward the drives.
This red (or sometimes blue) wire is connected to the number 1 pin on the drive's controller connector. (The number 1 pin is usually located next to the power connection.)
The CMOS settings for the A drive are the most likely cause. Always double-check the CMOS if you are experiencing a recurrent drive failure. Checking is quick, easy, and can save you time.
Yes, floppy disk controllers are sensitive to ESD (electrostatic discharge).
This error message indicates a failure to read the drive. These errors are the easiest to fix and can usually be attributed to a bad sector on the drive.
A voice coil actuator arm has several advantages over the stepper motor actuator arm. The lack of mechanical interface between the actuator arm and the motor provides consistent positioning accuracy. When the drive is shut down (the power is removed from the coil), the actuator arm (which is spring-loaded) moves back to its initial position, thus eliminating the need to park the head. In a sense, these drives are self-parking.
Hard disk drives are composed of one or more disks, or platters, on which data is stored. The geometry of a hard drive is the organization of data on these platters. Geometry determines the maximum storage capacity of the drive.
The geometry or type of many hard disk drives is labeled directly on the hard drive itself.
Head to Disk Interference (HDI) is another term for head crash.
The maximum number of heads is 16.
The maximum number of cylinders is 1024.
One sector holds 512 bytes of data.
The maximum number of sectors per track is 63.
CHS stands for cylinders, heads and tracks per sector.
The IDE is the standard drive on today's personal computers.
The first hard disk drives for personal computers used the ST-506/412 interface. The ST-506/412 was the only hard drive available for the IBM computer and the first to be supported by the ROM BIOS chip on the motherboard.
The Enhanced Small Device Interface (ESDI) was introduced in 1983 by the Maxtor Corporation. Beginning with this drive, most controller functions were incorporated directly onto the hard disk drive itself.
The Small Computer System Interface (SCSI) has been around since the mid 1970s in one or another form. Apple adopted the SCSI as its expansion bus standard. The SCSI bus functions as a communications pathway between the computer system bus and the SCSI device controller.
Partitions are logical divisions of a hard disk drive. A computer might have only one physical hard drive (called hard drive 0), but it can have anywhere from one to 24 logical drives, called C to Z.
There are two types of partitions: primary and extended.
A cluster is a combined set of contiguous sectors which the FAT treats as a single unit. The number of sectors in each cluster is determined by the size of the partition. There can never be more than 64,000 clusters.
The FAT (file allocation table) is simply an index that keeps track of which part of the file is stored in which sector. Each partition (or floppy disk) has two FATs stored near the beginning of the partition. These FATs are called FAT 1 and FAT 2. They are identical. Each FAT can be looked at as a two-column spreadsheet.
Fragmentation is the scattering of parts of the same disk file over different areas of the disk. When files are scattered all over a drive in noncontiguous clusters they are said to be fragmented.
To minimize the impact of a hard disk drive failure, perform comprehensive, frequent backups, and save a copy of the boot sector and partition table.
ScanDisk performs a battery of tests on a hard disk. These include looking for invalid filenames, invalid file dates and times, bad sectors, and invalid compression structures. In the file system, ScanDisk looks for lost clusters, invalid clusters, and cross-linked clusters.
The first method utilizes Logical Block Addressing (LBA mode)—a means of addressing the physical sectors on a hard disk drive in a linear fashion.
The second method utilizes Enhanced CHS—a standard that competes with LBA. This standard allows drives to be manufactured a little faster and more easily than LBA.
The third method utilizes Fast ATA, which uses PIO mode 3, and Fast ATA-2, which uses PIO mode 4.
The fourth method utilizes logical cylinders, heads, and sectors (L-CHS)—a value used by the operating system (for instance, MS-DOS, Windows 95 and Windows 98, OS/2) to determine the size of the hard drive.
The ATA standard requires each drive to activate its IRQ every time it sends one sector of data. This process helps to verify good data transmission, but it slows down the computer. Multiple block reads speed up the process by reading several sectors of data at a time.
Eight devices can be installed on a single SCSI-1 chain. However, one of those devices must be reserved for the SCSI controller. SCSI-2 and later host adapters allow up to 16, with one reserved for the host adapter. Some SCSI cards offer multichannel support and can handle even more.
Improper termination can cause a failure to boot, the "disappearance" of a device from the SCSI chain, erratic behavior, and—in extreme cases—can even destroy a SCSI device.
The BIOS protocol for SCSI devices is the Advanced SCSI Programmers Interface (ASPI).
Often, the only way to tell if there will be a conflict is to try the driver and see what happens. Remember to document every step you take so that you can undo any changes. Load only the device drivers for the SCSI devices.
If the problem occurs, use the F8 key to determine which driver conflicts. (Press F8 when starting MS-DOS or Windows 95 or Windows 98—this will allow step-by-step confirmation of the startup process.)
If the device driver is an executable file, try running it with the "/?" option. This will usually show a variety of command-line switches for the device driver (for example, "mouse.exe /?").
Advantages of using CD-ROM drives include: large storage capacity, sturdiness, portability, and the fact that data on the disk cannot be changed.
No, it is not. The 16X CD-ROM data transfer rate will be 16 times faster, but the mean access time is not 16 times faster.
You first have to determine whether or not there is room inside the case and if there are any available IDE controller connections. If not, then consider an external drive. If you want a SCSI controller, you will have to make sure there is an available slot in the expansion bus.
Windows 95 and Windows 98 use virtual drivers and do not need the MSCDEX.EXE real-mode driver. However, if you intend to use a CD-ROM drive in the MS-DOS mode (from a bootable disk), the real-mode drivers will have to be installed and added to the CONFIG.SYS and AUTOEXEC.BAT files of the boot disk.
A CD-ROM uses laser technology.
There are several ways to combine controller cards: use the secondary IDE controller on the motherboard; use a new controller card (supplied with the CD-ROM); use an existing SCSI chain; use a SCSI host adapter, create a new SCSI chain; or use an existing sound card with a CD connection.
The driver that came with the CD-ROM and the Microsoft MSCDEX.EXE program, are required for a CD-ROM drive installation.
Expansion slots on the motherboard are standardized connections that allow the installation of any device not soldered to the motherboard. By providing this connection to the expansion bus, computers can be customized to meet the requirements of the user.
The available expansion buses are: ISA, MCA, EISA, VESA, AGP, and PCI.
The computer will lock up.
There are 15 IRQs available, although some of them are permanently assigned.
If the first modem had been using COM1, the failure would be the result of an IRQ conflict. Devices assigned to COM1 and COM3 both make use of IRQ4. If the first modem has already been assigned to COM1, a conflict will occur when both modems make use of IRQ4.
One solution is to assign COM3 an available interrupt such as IRQ10.
The two divisions of the external data bus are the system bus and the expansion bus. The system bus supports the CPU, RAM, and other motherboard components. The system bus runs at speeds that support the CPU.
The expansion bus supports any add-on devices via the expansion slots and runs at a steady 7.16 MHz.
IBM established the ISA industry standard, thus generating the market for clones. The term ISA (Industry Standard Architecture) did not become official until 1990.
EISA uses a double slot connector that is compatible with ISA devices. Physically, the EISA bus is the same size and looks similar to the ISA. However, they differ in the number of contacts and the depth of the slot. On close inspection, you can see a double set of contacts (one above the other).
The Video Electronics Standards Association (VESA) is a trade association of display-adapter vendors. It was created to address the need for faster video to support the increased demands of new graphical operating systems like Windows and OS/2. These environments called for far better graphics and color management than the older character-based operating systems like CP/M.
Bus mastering allows a device to gain control of the bus to perform special tasks without processor intervention.
The PCI (Peripheral Component Interconnect) bus was designed by Intel to be a stronger, more flexible alternative to the current expansion buses while maintaining backward compatibility. It is independent of the CPU, so it is better than the VL bus and is not limited to use in 486-based computers.
The CPU uses the unique address (actually a block of addresses) to communicate with a device in the system using the bus.
The I/O port address of COM2 is 2F8.
An IRQ is used by a device to send a request to the CPU for permission to transmit data so that all devices do not attempt to communicate at the same time.
Here is a list of IRQ assignments. How many did you get?
|IRQ 0||System timer|
|IRQ 1||Keyboard controller|
|IRQ 3||COM2, COM4|
|IRQ 4||COM1, COM3|
|IRQ 6||Floppy disk controller|
|IRQ 8||Real-time clock|
|IRQ 13||Math coprocessor|
|IRQ 14||Primary IDE controller|
|IRQ 15||Secondary IDE controller|
The only function of the DMA chip (8237) is to move data. It handles all data passing from peripherals to RAM and vice versa.
If two devices have the same IRQ and try to communicate with the CPU at the same time, the resulting conflict will lock up the computer.
COM ports are for serial communications, and LPT ports are parallel ports normally used with printers.
Because these three things cause more conflicts than perhaps anything else in a computer, you will be able to reduce installation times and correct conflicts.
One dot of color is made up of three smaller dots: one red, one green, and one blue.
Interlacing is a way of arranging a video display so that the CRT sweeps all the odd-numbered rows and then all the even-numbered rows (or vice versa). The intention of interlacing is to reduce the flicker on the screen by increasing the refresh rate (in other words, scanning the screen twice as often). An interlaced monitor can be well-suited for stand-alone servers or computers that run for long hours unattended. It might be a good choice when there will be little interaction by an operator or when cost is a primary factor. Interlacing should be avoided for normal use, because it can lead to eyestrain and headaches.
The most basic form of power management is to turn off the monitor, using the power switch. At the same time, the CRT is the most expensive component of a monitor and can be damaged when it is turned on and off too frequently. Because these two concepts contradict each other, there is no single correct answer. You will have to make a decision based on the customer's individual circumstances.
Some variation of the SVGA video card is used on most computers sold today.
The formula is: video memory requirement = horizontal pixels x vertical pixels x color depth.
It stands for cathode-ray tube.
The number of times per second an electron beam sweeps is called the refresh rate. The speed at which the electron beam completes one horizontal trace is known as the horizontal refresh rate (HRR). The time taken by the monitor to complete all horizontal traces and return to the top of the screen is the vertical refresh rate (VRR).
Resolution is the measurement of image detail produced by a monitor or printer. Monitor resolution is expressed as the number of horizontal pixels by the number of vertical pixels.
With computer monitors, bandwidth is the maximum number of times per second an electron gun can be turned on and off. Bandwidth is measured in megahertz (MHz—millions of cycles per second). A typical value for a high-resolution, 17-inch color monitor would be around 100 MHz.
The CRT part of a monitor acts like a large capacitor and is capable of holding a very large charge (30,000 volts).
The video-signal cable, video controller card, video-driver software, and the monitor are the four primary sources of video problems.
Both offer dual port reads and writes, but WRAM is faster and less expensive.
Video data is displayed on the monitor by sweeping the electron gun(s) in a series of horizontal lines or traces across the display. The line created by each sweep is called a raster. The number of rasters is used to describe the vertical resolution of a monitor.
The PGA, VGA, and SVGA monitor each use a 15-pin, three-row, female DB connector.
Impact printers produce an image on paper by physically striking an inked ribbon against the surface of the paper. The advantages of impact printers are that they tend to be inexpensive and print at a relatively high speed. Impact printers were very popular in the late 1980s. Some disadvantages of impact printers are lower print quality and noise.
Ink-jet printers have replaced dot-matrix printers at the low end of the market. Many computer manufacturers and large computer stores offer ink-jet printers along with computers as part of package deals. They produce good-quality printing and are relatively fast, while requiring little maintenance beyond replacing the cartridge. What makes them attractive is their ability to easily produce color, as well as standard black-and-white images. High-quality color ink-jet printers are available; however, high-quality color printing comes at a cost. It requires a good printer and special paper that will prevent "wicking" of the ink, which causes a fuzzy appearance.
Laser printers have become one of the most popular types of printer for home use and are a must for most office environments. They produce high-quality, high-speed printing. Early laser printers were notorious for generating lots of heat and consuming lots of power.
A dot-matrix printer is an impact printer. Its main advantages are its ability to print forms (multiple pages) and its high reliability and low operating cost. Its disadvantages are its noise, slow speed, and generally low-quality (by today's standards) images.
Many of a laser printer's critical components, including those that experience the most wear and tear, are incorporated into the toner cartridge. The most important is the photosensitive drum. By incorporating these components into the toner cartridge, chances of failure are reduced because the primary-wear components are constantly replaced.
If residual particles remain on the drum, they will appear as random black spots and streaks on the next printed page. The drum will need to be cleaned to clear this problem.
There is a vast array of printers available and in order to ensure that you are obtaining optimum performance, the printer, the printer driver, and the software using the printer must be configured for the same mode. The IEEE 1284 standard establishes the standards to ensure printer compatibility.
Computers transfer data by means of parallel wires or buses. Computer modems use serial communication. Telephone systems use only two wires.
A modem is a peripheral device that enables computers to communicate with each other over conventional telephone lines and through wireless communication.
The ATH command takes the phone off the hook.
Baud is limited to 2400 cycles per second. Baud rate is limited by the capability of copper wires to transmit signals. Bps represents the actual number of data bits that can be transmitted per second.
This chip is called a UART (universal asynchronous receiver-transmitter).
Three protocols for synchronous communication are Xmodem, Ymodem, and Zmodem.
Zmodem shares all the features found in Xmodem and Ymodem protocols. It also adds a few new features, including crash recovery, automatic downloading, and a streaming file-transfer method. It is the protocol of choice for most telecommunication operations.
Handshaking is the negotiation of the rules (protocols) of communication between two modems.
AT commands are text commands that can be used to provide instructions to a modem. They are all preceded by the letters "AT." These commands are very useful as diagnostic tools for today's computer professional. To use these commands, make sure the communication software is loaded and the computer is in terminal mode. Unless the modem is set up to autoconnect (online mode), it will be in command mode and ready to accept AT commands.
In half-duplex, the RJ-11 plug has only two wires; therefore, only one signal can be sent or received at a time. Half-duplex is used to send messages in only one direction, like a fire alarm signal.
In full-duplex, the RJ-12 plug uses four wires (for two phones). It is the same size as the RJ-11 but with two additional wires. This enables users to send and receive data simultaneously.
Asynchronous communication is data transmission in which the length of time between characters may vary. Timing is dependent on the actual time it takes for the transfer to occur. This differs from synchronous communication, which is timed rigidly by an external clock.
Synchronous communication is a form of communication in which blocks of data are sent at strictly timed intervals. Because of this timing, no start or stop bits are required. Synchronous communication is more reliable than asynchronous and, therefore, more widely used.
Faxes involve a different technology from that used by modems and are developed by different standards committees and operate on technology defined in a different standard than modems. A fax can be a stand-alone machine or incorporated into a computer. Computer faxes allow you to use the same format as picture reproduction (they paint a page of black-and-white pixels).
Null-modem cables are used to directly connect two computers together without the need for a modem. The transmit and receive wires in the cable (wires 2 and 3) are switched to make the computers "think" they are using modems.
You should always consider the total operating cost, including the cost of paper and ink or toner.
Bps stands for bits per second.
Here is a table of connectors. How many did you get right?
|DB-9||Serial ports—external modem, mouse, printer.|
|DB-25||Parallel Port—printer, scanner, removable drive.|
|RJ-11||Standard telephone connector—2 wires.|
|RJ-12||Standard telephone connector—4 wires—used with dual phone connections.|
|PS/2 (mini-DIN)||Mouse, scanners.|
|USB||Universal serial bus—Technology that allows multiple peripherals to be attached to one cable.|
A 25-pin female connector is used for a parallel port on the computer.
The most common parallel connector on the printer is the Centronics connector.
Ohm's Law states that the current (electrons) flowing through a conductor, or resistance, is in linear proportion to the applied potential difference (volts).
The formula for Ohm's Law is voltage is equal to the current multiplied by the resistance (V = I R).
AC is alternating current in which the voltage varies from positive to negative. DC is direct current in which the voltage stays the same all the time.
The instrument used to measure the various components of electricity is VOM—Volt-Ohm Meter (sometimes referred to as DVOM or Digital Volt-Ohm Meter).
Continuity is a term used to indicate whether or not there is a connection from one point to another. It is used to determine the presence of breaks in wires and electrical circuits. If no continuity setting is available, use the resistance setting. If the multimeter measures infinite resistance, then there is no continuity, indicating a break in the circuit. If the multimeter shows little or no resistance, then there is continuity and the circuit is complete.
A power supply converts AC to DC voltage. When working properly, a pure DC signal will be produced. Sometimes, however, as the power supply ages, its ability to produce pure DC falters. A power supply uses capacitors to filter or smooth the voltage after being converted from AC to DC. These capacitors are second only to fuses as the part of a power supply most likely to fail. When a capacitor begins to fail, it allows more and more AC voltage to pass through. This AC voltage is superimposed on top of the DC voltage and is called noise or ripple.
To test for ripple, set a meter to read AC. Then connect a .1mfd capacitor to the red lead. With the power turned on, measure the DC voltage to ground. Any ripple present will be displayed as an AC voltage.
Just as high voltages generated by electrical and electronic equipment can do severe damage to humans, high voltages generated by humans can do damage to computers. We have all seen what a short circuit can do to electrical equipment (smoke, fire, and destruction). Electrostatic discharge (ESD) is an unseen (and sometimes unheard) force, created by humans, that is just as deadly to a computer.
The key to ESD prevention is to keep all electronic components and yourself at the same electrical potential. This usually means ground potential or zero volts. Maintain a habit of "grounding" yourself to the computer chassis whenever you attempt a repair. An ESD wrist strap is the tool most commonly used by technicians to prevent ESD.
This type of ESD problem occurs when a transistor junction becomes weakened. A transistor in this condition may pass all quality tests but, over time, will generate poorer system performance and eventually fail completely.
Catastrophic failure is the destruction of a part because of the heat generated during the mishandling and misapplication of a power source, cable, or test instrument.
It is never acceptable to use an AC power supply that is not grounded.
The basic toolkit should include screwdrivers, a Torx driver, tweezers, needlenose pliers, chip removers, a tube for small parts, a can of compressed air, ESD tools, a multimeter, a flashlight, a nut driver set, and curved hemostats.
A Torx driver is used to remove the star-shaped screws found on some proprietary computers. (Sizes T-10 and T-15 should meet the needs of most computers.)
One bootable floppy disk is needed for every operating system that you will be working on.
Always use ESD safety practices.
SIMMs (single inline memory modules) are provided in two basic (physical) formats: a 30-pin and a 72-pin chip.
You first have to determine whether there are any 30-pin slots available, then check the bus width to determine how many you will need to complete the job. For example, if the machine is a 486, you will need four modules to complete the job.
Parity is used to check the reliability of data. Parity requires one additional bit (chip). Memory can be purchased with or without parity. Parity adds about 10 percent more to the cost of memory. You cannot mix parity and nonparity chips.
L1 cache is part of the CPU and cannot be upgraded.
First, the machine must have an available expansion slot. Second, there must be available resources such as IRQ and an address.
It will probably work, but will have to be manually configured either through software or jumpers.
First, you must evaluate the existing motherboard to see if it can be upgraded and then determine the highest CPU that you can use. Second, you must determine the needs of the customer, particularly whether the CPU upgrade will meet the customer's operational requirements.
Plug and Play, the latest technology available for installing expansion cards, is an independent set of specifications developed by a group of hardware and software companies. This specification allows the user to make configuration changes with minimal adjustments. The user simply installs the card, turns on the computer, and uses the device.
DOS stands for disk operating system.
The original version of DOS was designed to support the operation of floppy disk drives.
The version bundled with Windows 95 is referred to as MS-DOS 7.0.
From the command prompt in the root directory, the MS-DOS command DIR or directory will return the list of all the files on the drive and indicate the amount of free space available.
MS-DOS operates with a 1-MB memory limit. This is called real mode. Windows broke out of the MS-DOS 1-MB barrier by engaging 286-level protected mode (Windows 2.0). Protected mode Windows could address up to 16 MB of RAM. Although MS-DOS programs could run only in the first megabyte of memory, specialized programs were written that would run in (and only in) the extended memory controlled by Windows. Protected mode refers to using protected memory.
GUI stands for graphical user interface. MS-DOS used a text or command-line interface. With MS-DOS, you had to memorize and type commands. With a GUI interface, you work in a graphical environment and use a mouse with icons or menus to simplify tasks.
Windows provides three types of font files. Each font contains a complete character set for a particular typeface.
Many settings can be changed from the Windows Control Panel.
Some of these are Screen colors, Other desktop options (screen savers, wallpaper, and so on), Fonts, Printer, Keyboard, Mouse, International settings, COM port settings, Network settings, Date and Time, Sounds (used by the system), Drivers for hardware, and Multitasking and virtual-memory settings.
The single character wildcard is the question mark (?).
Installing devices, managing memory, optimizing the system, and troubleshooting are handled differently in Windows 95 than in Windows 3.x.
The ultimate goal of any computer user is to be able to simply plug any device into a computer, turn it on, and have it work. This is the concept upon which Plug and Play is founded. A well-designed Plug and Play system eliminates the need for jumpers, switches, and installation software.
The three requirements of Plug and Play are: a Plug and Play BIOS, a Plug and Play device, and a Plug and Play operating system (such as Windows 95).
Windows 95 does not require MS-DOS. MS-DOS is provided mostly for backward compatibility.
DOS 7.0 comes with Windows 95.
CONFIG.SYS is not required to install GUI drivers; however, it is required if you want to use any real-mode drives.
The VCACHE that comes with Windows 95 is quite different from Windows 3.x in that the cache is "sized dynamically." As Windows needs more RAM, it takes away from the cache and vice versa. Unfortunately, the cache-sizing algorithms are very slow, especially when used with the swap file; therefore, the swap file needs to be limited in size.
Windows 3.x is basically an operating environment created to run on top of MS-DOS; its purpose is to provide a GUI and other features in order to run programs and manage files easily. Windows 95 is a complete operating system that includes an improved GUI as well as other useful features.
Older disk utilities do not understand many of the improvements of Windows 95, such as long filenames.
The first step in the boot-up process is to run the POST.
MS-DOS external commands reside in the windows\command directory of the bootable drive.
FDISK for Windows 95 is no different than for Windows 3.x; it is used to partition hard drives. Windows 95 OSR2 and Windows 98 do give the option of using FAT32 file system instead of FAT16.
Virtual memory uses disk space to simulate RAM. This hard disk drive space is called the swap file.
The two binary files that hold the Registry database are called SYSTEM.DAT and USER.DAT.
An MS-DOS session runs inside a window in the GUI. Windows 95 has the new MS-DOS mode that allows creation of custom CONFIG.SYS and AUTOEXEC.BAT files for tough MS-DOS applications. MS-DOS mode exits the GUI—therefore, you might have to configure real-mode drivers to access hardware.
You must create (or edit) the CONFIG.SYS and AUTOEXEC.BAT files to load the appropriate real-mode drivers for the CD-ROM. You will also need to run the MSCDEX.EXE application.
Windows 95 no longer creates .PIF files by using the PIF editor. PIF settings are created by accessing the Properties value that appears when an MS-DOS application is right-clicked.
The five steps are startup and system check; information collection; hardware detection; startup disk creation and file installation; and windows configuration.
Only the OSR2 version uses FAT32.
Safe mode starts Windows 95 with a minimum of drivers. This mode is considered to be the Windows 95 troubleshooting mode.
The three primary Registry backup tools available in Windows 95 are: Microsoft Configuration Backup (CFGBACK.EXE), Emergency Recovery Utility (ERU.EXE), and REG files.
Windows Explorer replaced the Windows 3.x File Manager—the more advanced Explorer is the better choice for computer professionals.
Windows 95 uses two programs for managing files: My Computer and Windows Explorer.
Use the FDISK program that came with Windows 95 to partition hard disk drives.
The Recycle Bin provides temporary storage for discarded or deleted files.
The System Monitor provides real-time reports on how different system processes are performing. It displays various functions using either a line graph, a bar graph, or a numeric graph.
The Resource Meter is used to monitor the use of system resources in real time. When activated, it adds a small bar graph to the taskbar (in the notification area) that indicates the percent of free resources (based on the computer's total resources).
With SETVER.EXE loaded, Windows 95 will report a compatible version number to your MS-DOS application.
Your best protection is to acquire and use an antivirus program. Remember to keep it up-to-date as new viruses are created every day.
The three basic elements required to create a network are connection, communication, and services.
In addition to the ability to share resources, LANs are resilient, act as communication gateways, and facilitate electronic mail.
In a peer-to-peer network, each computer acts as a server or a client depending on the user's needs. Each user, or workstation, establishes its own security and determines which resources are available to other users.
In a server network, a central server (dedicated computer) manages access to all shared files and peripherals. This is a secure environment suitable for most organizations.
The three network topologies are star, bus, and ring.
Thin Ethernet uses a round BNC connector and UTP uses an RJ-45 connector (similar to a telephone jack).
Network interface cards (NICs) link the computer to the network cable system. They provide the physical connection between the computer's expansion bus and the network cabling.
A network protocol is a set of rules governing the way computers communicate over a network. In order for computers using different software to communicate, they must follow the same set of networking rules and agreements, or protocols. A protocol is like a language. Unless both computers trying to communicate are "speaking" and "listening" in the same language, no communication will take place.
Bridges work like repeaters but offer additional advantages. They can isolate network traffic or problems. The traffic within a segment will not be sent to the entire network unless its destination is in another segment. Bridges can also link unlike segments (Ethernet and token ring).
Routers provide interconnectivity between like and unlike devices on the LAN and WAN. Routers work like bridges, but can connect networks using different protocols and can select the best route from network to network based on traffic load. Routers route data based on factors such as least-cost, minimum delay, minimum distance, and least congestion. Routers are generally used to create a wide area network and to connect dissimilar networks.
Gateways provide as much interconnectivity and even greater functionality than routers and bridges do. A gateway usually resides on a dedicated computer that acts as a translator between two completely dissimilar systems or applications. Since a gateway is both a translator and a router, it tends to be slower than bridges or routers. Gateways also provide access to special services such as e-mail or fax functions.
TCP/IP is the most widely used network protocol. It is the protocol of the Internet.
A LAN is a local area network; it is usually confined to a limited space such as a building or a room. A WAN is a wide area network and can span long distances (even worldwide).
This type of problem is called a bottleneck. A bottleneck on a system is the resource that limits the rate at which a task can be completed. If your task uses the processor, network and disk resources, and spends more of its time transferring data to and from the disk, you might have a memory bottleneck. A memory bottleneck might require adding more RAM.
An ISP (Internet Service Provider) provides the connection between dial-up (modem) users and the Internet.
Here is a table of common Internet domain extensions. How many did you get?
|.gov||US Government nonmilitary institutions|
|.mil||US Government armed services|
|.xx||Two-letter country code|
URL stands for Uniform Resource Locator, the address system used on the World Wide Web.
Other certifications available are Novell CNN and CNE, or Microsoft MCP and MCSE.
The three types of portable computers are laptop, notebook, and subnotebook or palmtop computers.
Docking stations (also known as docking ports) are specialized cases that allow entire notebook computers to be inserted within them. This allows the notebook to be connected to desktop I/O devices such as full-sized keyboards, CRT monitors, and network connections.
In order for laptop and notebook computers to have the same degree of expandability that is associated with desktop computers, the Personal Computer Memory Card International Association (PCMCIA) established several standards for credit-card-sized expansion boards that fit into small slots on laptop and notebook computers.
There are four types of PCMCIA cards:
PCMCIA (PC-Card) is part of the Plug and Play standard. Plug and Play-compatibility means being able to add components without turning off or rebooting the computer. PCMCIA buses are not configured with jumper settings (because they don't have any) but with software.
The two types of displays found on laptop computers are active-matrix and dual-scan.
In desktop systems, CPU heat is dissipated with the use of cooling fans housed inside the case. There is no room for this solution in a portable system, so manufacturers have addressed this problem in the packaging of the chip itself.
Except for the size and packaging, hard disk drive technology is similar to desktop technology. EIDE drives are standard in portables, with the exception of Macintosh, which uses SCSI.
A cleaning kit should contain at least the following: lint-free cloth, cleaning solution, foam swabs, and antistatic spray.
ESD (electrostatic discharge) will destroy electronic components.
Yes, a properly grounded computer will help prevent EMI (electromagnetic interference).
Never work above your skill level when it comes to safety! Working inside the monitor case should be left to a properly trained technician with the necessary tools to protect against high voltages.
The power switch on some computers, usually located on the front of the computer, uses 110 volts AC to turn the power supply on or off. If you are working on a computer and it is plugged in to provide proper grounding, this could present a hazard.
Type C fire extinguishers are used for electrical fires.
To clean a keyboard, use a hand-held vacuum to remove dust from the small crevasses.
To clean a laser printer, complete the following steps:
Examples of recyclable items that require special disposal are batteries, toner and cartridge kits, circuit boards, chemical solvents, and monitors (CRTs).
Often the manufacturer provides a prepaid shipping box to return the cartridge.
When purchasing or using any kinds of chemicals (for instance, cleaners) be sure to look at the MSDS (material safety data sheet). This form describes the nature of any chemicals manufactured. It includes generic information about the chemical makeup and any recognized hazards of the product (along with what to do and who to call if there is a problem).
Five ways to stay on top of your profession are to: keep learning; network with others; take advantage of opportunities to connect with your peers through professional groups and trade shows; practice your skills; and read widely.
The unlimited free technical telephone support that we once took for granted is being replaced by support offered through e-mail and the Web. This means that increasingly we are expected to get the job done without free direct phone support from the original equipment manufacturer (OEM). Technical support is out there, but it must be used wisely to be cost-effective.
Four categories of tools used by computer technicians include hardware toolkit, software toolkit, spare parts, and access to a technical library.
The bare minimum software toolkit should include: ATTRIB.EXE; DEFRAG.EXE; EDIT.COM; EMM386.EXE; EXPAND.COM; FDISK.EXE (.COM); FORMAT.EXE (.COM); HIMEM.SYS; LABEL.COM; MEM.EXE; Memmaker; MSCDEX.EXE; MSD.EXE (.COM); QBASIC.EXE; SCANDISK.EXE; SHARE.EXE; SIZER.EXE; SMARTDRV.EXE; and SYS.COM.
Phase 1 is to define the problem.
Phase 2 is to identify the cause.
Phase 3 is to make the repair.
Phase 4 is to confirm the repair.
Phase 5 is to document the incident.
Good recordkeeping is essential if you are to become a success at your profession. Recordkeeping is the process by which you keep track of which techniques worked and which did not work. In short, it becomes your experience database. Good records will save you valuable time in the long run.
Level 1 is to provide local support by assigning a knowledgeable person onsite to address minor problems.
Level 2 is to provide telephone support.
Level 3 is to provide on-site support.
Standardization of equipment in large companies reduces the number of spare parts required and simplifies installations.
The four stages of a service call are the greeting, the description, the interview, and the closing.
If the individual needs training, ensure that they have information about available courses.
If the individual is a coworker, speak to the person who supervises them and identify their training needs.
If the individual is a client, gently suggest that it would be beneficial to obtain specific training.
Send the client a memo or instruction sheet to follow. Save the instructions for future use.
Dealing with technophiles (or those who think they are experts) can be a challenge. The best option is to listen carefully and make the individual part of the solution, not part of the problem. Remember, they came to you for help.
In a corporate setting, form an advanced users group and give participants responsibility for finding solutions to issues. Ask coworkers (or users) who constantly complain about trivial problems to put all complaints in writing. Keep their notes as part of your records.