Accelerator
board
1. A circuit board containing one or more 680x0, PowerPC, or other processors
used to upgrade the CPU and/or graphics performance of a Macintosh computer.
2.
Circuit board upgrading performance in a particular area of PC funtionality,
typically graphics.
Access
time
A measurement of the average time it takes from when the PC issues a command to
get data from a disk drive. This is a combination of several factors. The major
determining factor is drive seek time. Moving the read/ write heads is the
slowest, single operation for a hard disk. The faster it can move the head
array during seek time, the faster the disk access time.
Add-on
board
A circuit board that changes or improves a personal computer's capabilities.
For example, a memory board increases the amount of RAM in a computer. A
network board (also called an NIC or network adapter card) lets workstations communicate
with each other and the NetWare server. These boards are connected by cabling
or some other transmission medium.
Address
space
A block of addresses that a process can assign to a particular block of data.
The memory allocated from an address space must be backed by physical memory.
Analog
The representation of a continuously changing physical variable (sound, for
example) by another physical variable (such as electrical current).
Analog
adapter
On an analog video board, intensity information is transmitted across separate
lines, one for each of the three primary colors (red, green and blue). In
theory, the possible number of variations of each of the basic colors could
allow for an infinite number of displayed color variations. VGA, Super VGA, MCGA,
and 8514/A monitors require analog adapters.
ANSI
character set
The American National Standards Institute 8-bit character set containing 256
characters.
Apple
Desktop Bus (ADB)
The expansion bus used to connect Macintosh keyboards and input devices.
Architecture
The specific design and construction of a computer. Architecture usually refers
to the hardware makeup of the central processing unit and the size of the byte
or set of bytes it processes, such as 8-bit, 16-bit, or 32-bit architecture.
ASCII
terminal
A terminal that uses ASCII. Usually synonymous with asynchronous terminal and
dumb terminal.
Asynchronous
modem
A modem that cannot supply timing signals and requires all the timing
information to be supplied by the associated data terminal equipment (DTE).
Asynchronous
transmission
In computer communications, data (binary digits) can be transmitted in
asynchronous mode or synchronous mode. When the mode is asynchronous, the
binary digits are not orderly, meaning they are out of synchronization and sent
at irregular intervals in characters, words, or blocks. To ensure that the
receiving device is ready, a special start bit is sent ahead of each character
and a stop bit at the end of each character, a process which continues until
the final character is sent. In ASCII, where 8 bits form a character or byte,
10 bits must be sent for each character. Asynchronous transmission is sometimes
known as start-stop transmission.
Automatic
Baud Rate Detection (ABR)
Sometimes referred to as Autobaud, it is a process by which a receiving device
determines the speed, code level, and stop bits of incoming data by examining
the first character, which is usually a pre-selected sign-on character. ABR
allows the receiving device to accept data from a variety of transmitting
devices operating at different speeds, without the need to establish data rates
in advance.
Backup
1. Pertaining to a system, device, file, or facility that can be used to
recover data in the event of a malfunction or loss of data.
2. To copy information, usually onto diskette or tape, for safekeeping.
Baud
rate
The data transmission speed setting of a serial device. Typical rates include
300, 1,200, 2,400, 9,600. Higher speeds, 19,200, 38,400, and 57,600 baud, are
achieved through data compression. Sometimes referred to simply as baud.
Binary
Having two components or possible states. Usually represented by a code of
zeros and ones.
Binary
Digits (bit)
A computer only knows two states: ON and OFF. Each bit is either a one (1), or
zero (0). The Binary Digit 1 represents "ON," while the number 0
represents "OFF." The term "bit" is derived from Binary
DigIT. Eight bits make up a byte. The American Standard Code for Information
Interchange (ASCII) character set is used to translate bits into characters and
numbers. In this standard, 1 byte is used to represent each letter of the
alphabet, for example, "01000001" represents the letter
"A."
Block
The smallest amount of disk space that can be allocated at one time from a disk
partition or volume. Block size is determined by disk size, operating system,
and file system type.
Buffer
A temporary storage place for information. Many times it is a device used to
compensate for a difference in either the rate of data flow or the time of
occurrence of events in transmission from one device to another.
Bus
1. A pathway on which data travels. Examples of buses in a typical Macintosh
computer include the expansion bus (NuBus or PCI), Apple Desktop Bus (ADB), and
SCSI bus. 2. LAN data pathway based on a single cable terminated at both ends.
Byte
Short for "binary digit eight." A unit of information consisting of
usually 8 bits. A file's size is measured in bytes or potential storage
capacity is measured in bytes, but when dealing with very large numbers, the
terms kilobyte, megabyte, or gigabyte are used.
Bytes
per second (Bps)
Usually the number of bytes which can be transmitted or transferred each
second.
Cache
An area of computer memory set aside for frequently used data to speed
operations. Some caches are general purpose, while others are for specific
operations. A disk cache is an area of system memory reserved for caching disk
reads and writes. A CPU cache is a dedicated, high-speed memory array used to
cache pending instructions.
Cache
memory
This is a dedicated area of RAM memory used for temporary storage of data. It
provides faster access and typically improves overall performance. This is a
function of most operating systems and many applications. The specific content
of the cache memory is operating-system and application specific.
Cartridge
Fonts
A plug-in ROM cartridge that installs in a printer and supplies additional
fonts for printing.
Cathode
Ray Tube (CRT)
An output device consisting of a television-like screen used for displaying the
letters, numbers, or graphic output of a computer. Most personal computers use
a monitor based on CRT technology.
Character
set
A set of acceptable and recognizable characters used by a particular computer
system or software package. Character sets are binary-coded, and often follow a
standard such as ASCII, ANSI, or EBCDIC.
Circuit
1. In data communications, a circuit is a means of bidirectional communication
between two points, consisting of transmit and receive channels.
2. In electronic design, a circuit is one or more components that act together
to perform one or more functions.
Clock
speed
The speed (in megahertz) of a processor's primary clock oscillator.
Cluster
A group of data stored together on one or more sectors of a floppy disk or hard
disk. (A sector usually contains 512 bytes of data.) When DOS stores data on a
disk, it usually breaks the data into smaller sections which it writes to
various places on the disk as appropriate.
CMOS
RAM
This memory stores system configuration data, for example the number of drives,
types of drives, and amount ofmemory. It is battery-powered, so it can retain
the data, time, and other information that must be stored when the computer is
turned off.
Color
Graphics Adapter (CGA)
An older monitor technology, CGA was IBM's first attempt at a color monitor for
the PC. The CGA had 3 wires representing the three primary colors (red, green,
and blue) plus one wire for intensity. Together these 4 wires produced color on
the display.
COM
port
A connection on the computer where the cable for a serial device is attached.
The serial device could be a printer, network interface card, modem, or other
device. COM ports are often called serial ports. COM ports are numbered, and
generally COM1 through COM4 are supported on most personal computers. It is
possible to have more or less than four COM ports.
Compact
Disc Read-only Memory (CD-ROM)
A read-only optical disc commonly used to distribute applications software or
archive data.
Complementary
Metal Oxide Semiconductor (CMOS)
A specialized memory chip, powered by a small battery, that stores basic system
configuration information.
Component
Hardware or software that is part of a functional unit.
Control
Unit (CU)
In the processor, the CU is the part that retrieves instructions in proper
sequence, interprets each instruction, and applies the proper signals to the
arithmetic logic unit and other parts in accordance with this
interpretation.Also, one of two parts of the Central Processing Unit (CPU)
containing circuits that, with electrical signals, direct and coordinate the
entire computer system.
Controller
board
A device, also called a host bus adapter (HBA), that allows a computer to
communicate with another device, such as a hard disk or tape drive. It manages
input/output and regulates the operating of the other device.
Conventional
Memory
The first 640 KB of memory in a PC is called conventional or base memory. It is
used to load the DOS command processor, device drivers, and Terminate and Stay
Resident (TSR) programs. It is also used by DOS applications.
Coprocessor
An auxiliary processor designed to relieve the demand on the main processor by
performing a few specific tasks such as floating point math or graphics
calculations. In general, coprocessors handle tasks that would be performed
more slowly by the main processor.
Crash
A system failure or "bomb." A system crash requires that the user
perform a reboot to restart the computer.
Cylinder
On a disk drive, a cylinder is the data area that can be accessed by all the
drive's read/write heads while they are lined up in a single position. When the
gang-mounted read/write heads move to a position on one platter, they all move
to the same position on every platter. Gang-mounted means that they are moved
in unison.
Data
1. In a database, facts about places, individuals, objects, events, concepts
and so on.
2. Used to refer to any stored information.
Data
communication
The transfer of data from one device to another via direct cabling;
telecommunications links involving modems, a telephone network, or other
connection methods. Transfer of information between functional units by means
of data transmission according to a protocol.
Device
Any computer peripheral or hardware component (such as printer, mouse, monitor,
or disk drive) capable of receiving and/or sending data, generally through the
use of a device driver.
Device
driver
Hardware-specific software that acts as an interface between the operating
system and the hardware attached to a computer. Device drivers allow
applications to communicate with hardware in a controlled and orderly fashion.
A device driver is installed when the system is initialized, either by the
operating system or through an installable device driver. Some examples of
installable device drivers are mouse, graphical/video monitor, communications
port, printer, and network interface card.
Digital
Devices that represent data in the form of digits, based on the binary system
where the binary digits (bits) are zero or one. Also, pertaining to data that
consists of digits.
Direct
Memory Access
Direct Memory Access (DMA) channels allow devices to communicate directly with
memory. This is generally used with add-in boards or devices that transfer
large amounts of data. Examples include network interface cards, CD-ROMs, and
sound cards. IBM XT-style systems have four available DMA channels (0 through
3). ISA/AT, MCA, and EISA systems have eight DMA channels (0 through 7). Each
device that uses DMA must have its own unique DMA channel. Channel 0 is
available in ISA/AT-type systems. and above. Channel 1 is used for the disk
controller in XT systems, but is available for AT-style systems and above. DMA
channel 2 is used for the floppy disk controller. Channels 3 through 7 are
available for use. For some devices, use of a DMA channel may be optional, but
will normally result in improved performance.
Disk
A circular object with a magnetic surface used to store files (programs and
documents) on a computer. For example, a floppy or hard disk.
Disk
drive
A magnetic or optical device used to store files and folders. Types of disk
drives include fixed (hard) disks, floppy disks, and removable media such as
Syquest, Jaz, Zip, and magneto-optical (MO) disks.
Disk
driver
Disk driver##1. Software device driver allowing the operating system to
communicate with a hard disk controller. 2. NetWare NLM (with a DSK extension)
that interfaces between the NetWare server operating system and the hard disk
controller. The disk driver communicates with an adapter connected to the disk
drives. Depending on the type, one or more disk drives can be connected.
Drivers are loaded into the operating system during installation or at the
command line.
Disk
duplexing
Disk duplexing is an implementation of Redundant Arrays of Independent Disks
(RAID) Level 1 and is similar to disk mirroring. It uses two disk drives that
are configured to have the same logical size. Both drives are connected to
separate disk controllers. During each data write, the same data is written to
both disks.
Disk
I/O performance is generally better than when using disk striping with parity.
Performance is better during data reads than with disk mirroring. The boot
partition (active system partition) can be duplexed. Disk duplexing is designed
to keep a network going in spite of disk errors or the loss of a hard disk. If
a read error occurs, data from the other disk is used. If one drive or
controller fails, the server will continue running by using the other drive and
controller. Users can continue to work without interruption. Disk duplexing is
normally used on peer-to-peer networks and smaller LANs for the protection of
critical data files. Due to the amount of storage lost through redundancy, it
is not commonly used on larger LANs.
Disk
mirroring
Disk mirroring is an implementation of Redundant Arrays of Independent Disks
(RAID) Level 1. It uses two disk drives configured with equal-sized partitions
and connected to the same disk controller. During each data write, the same
data is written to both disk partitions.
With
disk mirroring, disk utilization is 50% of the dedicated storage space. I/O
performance generally is better than when using disk striping with parity. A
mirrored pair can be split without loss of data. Disk mirroring is designed to
keep the computer operationalyou going in spite of disk errors or loss of a
hard disk. If a read error occurs, data from the other disk is used. If one
drive fails, the server will continue running by using the other drive. Use
disk mirroring when data must be protected against drive failures, and hard
disk resources are and will be plentiful as system requirements grow. Disk
mirroring is normally used on peer-to-peer networks and smaller LANs to protect
critical data files. Due to the amount of storage lost through redundancy, it
is not commonly used on larger LANs.
Disk
Operating System (DOS)
The software programs that control the operation of the computer and the
movement of information throughout the computer system. DOS is the medium by
which the user communicates with the computer system and manipulates data.
Disk
Partitioning
Hard disk initialization takes care of the physical preparation of the hard
disk. The logical disk preparation must also be completed. This involves
partitioning the hard disk. When a hard disk is partitioned, logical divisions
are created on the hard disk. This makes the disk storage areas available to
the system. Multiple partitions may be created on the same hard disk, including
partitions for different operating systems. For example, a hard disk may set up
as an OS/2 dual boot system with both DOS and OS/2 disk partitions.
Partitioning creates a partition table for each partition. The partition table
contains information such as the partition type (operating system), size, and
any logical drives configured within the partition. When the disk is
partitioned, the active partition must be identified. This is the partition
that is read by the system during system startup. The active partition is also
referred to as the boot (bootable) partition. Disk partitions may be changed at
any time, but extreme care must be taken. Creating, deleting, or modifying the
size of disk partitions will cause all of the information in the affected
partitions to be lost. Disk Striping##A method of spreading data evenly across
multiple physical hard disks.
Disk
Striping with Parityx
Disk striping is an implementation of Redundant Arrays of Independent Disks
(RAID) Level 5. Microsoft Windows NT Server does the same thing as commercial
RAID drive arrays, but through software rather than hardware. Between 3 and 32
disk drives may be included in an NT Server stripe set. The disk space used on
each drive will be approximately the same. NT Server will match the space
selected to the smallest single partition when the stripe set is created. Disk
striping provides improved performance on disk reads. Disk utilization is
reduced by the size of one disk drive. Data and parity is spread across all of
the drives in a stripe set. As data is written, it passes through an algorithm
to generate the information for the parity stripe.
The
way data clusters are organized, large data files tend to get written across
multiple drives. There is a loss in write performance, however, this is made up
by splitting read requests, giving excellent read performance and improved data
security. Possibly more important is the data security aspect. If a drive is
lost, the system can recover any missing data by going through its calculations
on the remaining data and parity stripes. When this happens, read performance
suffers. All of the data can be re-created, when the drive is replaced. When
implementing disk striping without parity, data is written to the drives in
much the same manner. The major difference is that the stripe used here for
parity is instead used for additional data storage. One thing to remember is
that the boot partition (active system partition) cannot be a stripe set. Disk
striping with parity is normally used on large networks where data integrity
and minimized down time are critical concerns. While the amount of storage
space lost can be significant, as more drives are added, the percentage of
space lost to parity becomes less. Use disk striping with parity when multiple
hard disks are available, optimal read performance is desired, and data
integrity is a critical concern. You are protected against the failure of any
one drive. A failing drive should be replaced as soon as possible, even though
the users can continue working after the failure. Performance will be the same
on disk writes, but will degrade on disk reads. When performance is the
overriding concern and budget constraints allow, you should install a RAID disk
subsystem rather than configuring discrete hard disks through disk striping
with parity. A RAID disk subsystem, though more expensive, will provide
significantly better performance. Display Adapter##The circuitry used to drive
a video display monitor. Some computers include the video adapter circuitry on
the system board while others require an expansion card. There are two formats
with which data may be sent from the adapter to the display: analog or digital.
Dots
per inch (dpi)
A measurement (dpi) of the resolution of a video display monitor, printer or
other output device.
Double-Density
(DD)
Density refers to how tightly data can be recorded on the media. The name,
"Double-Density (DD)," came from recording improvements over the
original method. The capacity of the diskette was effectively doubled.
Double-Sided
(DS)
For diskettes, the ability to write to both sides of the diskette medium is
called double-sided (DS).
Double-Sided,
Double-Density (DSDD)
DSDD can refer to both the medium being used, a DSDD floppy diskette for
example, and the drive's mechanical recording capabilities, a DSDD floppy
diskette drive.
Double-Sided,
High-Density (DSHD)
DSHD can refer to both the medium being used, a DSHD floppy diskette for
example, and the drive's mechanical recording capabilities, a DSHD floppy
diskette drive.
Downloadable
font
Also known as soft font, an electronically represented printer font (a graphic
design of characters and symbols) which must be installed on the computer and
sent to a printer before it can be printed.
Drive
Type
The drive type number is placed in a table stored in the computer's CMOS
memory. The table identifies the drive and its characteristics (number of
read/write heads, storage capacity, number of cylinders, number of sectors per
track, etc.) so that the operating system knows how to access the drive.
Driver
Software used to allow the operating system to communicate with an add-on
hardware device such as a disk controller or display adapter.
Dual,
In-line Memory Module (DIMM)
A high-density, 168-pin module used to package RAM.
Dumb
terminal
A workstation consisting of keyboard and monitor. A dumb terminal is used to
put data into the computer or receive information from the computer. Dumb
terminals were originally developed to be connected to computers running a
multiuser operating system so that users could communicate directly with them.
All processing is done at and by the computer, not the dumb terminal. In
contrast, a smart terminal contains processing circuits which can receive data
from the host computer and later carry out independent processing operations.
Dump
Backup of a database or transaction log onto another device whether it be the
same or different media. Dumps are used for regularly scheduled backups or to
recover from media failures.
Dynamic
Random Access Memory (DRAM)
The most commonly used memory type for personal computers. Because of its passive
componentry design, DRAM requires a periodic refresh signal to maintain valid
data.
Electron
gun
Enclosed in the CRT, the electron gun produces a beam that fires at the
phosphor elements on the screen, causing them to produce a single pixel of
light on the display. The electron gun is controlled by the incoming digitized
or analog data sent from the adapter.
Enhanced
Graphics Adapter (EGA)
EGA was introduced as an enhancement to the first color display for PCs (CGA).
The EGA was equipped with two more wires providing intensity for each of the
three primary colors and the ability to produce more color combinations. Also,
the horizontal scanning frequency was synchronized for a much clearer output
display.
Error
control
An arrangement that combines error detection and error correction.
Error
correction
Error correction##A method used to correct erroneous data produced during data
transmission, transfer, or storage.
Expanded
Memory (
The Expanded Memory Specification (EMS) was created when PC processors were
limited to 1 MB of Random Access Memory (RAM). Spreadsheet users needed a way
to create extremely large spreadsheets and could not do this in the 640 KB
available in PCs of that era. A way to work around this memory limitation was
needed. To answer this need, Lotus, Intel, and Microsoft (LIM) developed the
Expanded Memory Specification. This specification utilized a special
Eventually,
the special
Expansion
slots
Electrical connectors on the system board that allow additional hardware to be
added to the computer. PCs can include 8- or 16-bit ISA, EISA, MCA, Vesa
LocalBus, or PCI slots, or a mixture of ISA and any other slot type. Macintosh
computers provide either NuBus or PCI slots. Extended Memory (XMS) Extended
Memory (XMS) is all memory above 1 MB (1024 KB). Intel 80286 processors were
limited to 16 MB of extended memory. This was increased to 4 GB in the 80386
and later processors.
DOS
systems must have an extended memory manager, such as HIMEM.SYS, loaded to
access this area of memory. XMS memory can be used for applications, disk
caching, and Expanded Memory (EMS) emulation. The official XMS specification,
"Extended Memory Specification Version 3.0," is available from
Microsoft at ftp.microsoft.com/softlib/ mslfiles. Extended memory manager##A
program that prevents different applications from using the same part of
extended memory at the same time.
Fault
tolerance
Operating systems features designed to accommodate failures, therefore
improving disk reliability. Related terms are "Disk Mirroring,"
"Disk Duplexing," and "Disk Striping with Parity."
Flicker
The noticeable flashes seen while viewing a screen display. The rate at which
the screen is scanned and refreshed as well as the persistence of the phosphor
coating on the monitor to hold the light. Monitors are designed to operate at
different refresh rates; slower rates produce a significant flicker. The
flicker is a result of too much time elapsing before the image is refreshed;
therefore, the image begins to decay.
Floating
Point Processor
A microprocessor that has been optimized to perform floating point math
operations such as trigonometric functions.
Floating
Point Unit
Another term used to describe a floating point processor.
Floppy
disk
A magnetically sensitive, flexible disk used as a secondary storage medium. The
two most common sizes are the 3-1/2-inch disk which is fully enclosed in a
rigid plastic casing and the 5-1/4-inch floppy disk.
Floppy
drive
A device which stores data externally on small portable devices called
"floppies." Floppies come in different sizes and hold different
amounts of data. The two most common sizes are the 5-1/4-inch and the
3-1/2-inch.
Frequency
The number of times one complete incident or function occurs. In electronics,
frequency usually refers to the number of waveforms that are repeated per
second, measured in Hertz.
Full-height
Full-height describes the size, in height, of the drive. Full-height drives
originated in the IBM PC and XT models. They are roughly 3 inches in height.
Half-height
Half-height describes the size, in height, of the drive. Drives that are
half-height are half the height of full- height drives. Half-height drives are
about 1-1/2 inches in height. Two half-height drives can fit in a full-height
drive bay.
Handshaking
Before data is transmitted serially, certain communications conditions, or
protocols, must be met. Handshaking allows both the sending and receiving
computers to understand the required signals, i.e., the method of transmission.
Hard
disk
1. A peripheral mass-storage device that uses sealed, rotating, nonflexible,
magnetically coated disks to store data and program files. Hard disk types
include SCSI, IDE, and EIDE.
2. A magnetic storage device based on the original
Hard
Disk Controller
The board that communicates with and controls the hard (fixed) disk drive.
Hard
Disk Encoding
A method of compression of data within the hard disk drive. An example is MFM
or RLL. Hard disk encoding is mostly used in older devices.
Hard
Disk Interface
The communication device which allows the hard disk drive to interact with the
hard disk controller. There are many different types which will affect the
speed of data transfers. Examples of hard disk interfaces are ST506, SCSI,
ESDI, and IDE.
Hardcopy
Sending computer data out to the printer and printing the information on paper
is referred to as producing hardcopy, or a copy on paper which can be
physically handled.
Hardware
All electronic components of a computer system, including peripherals, circuit
boards, and input and output devices. Hardware is the physical equipment, as
opposed to software consisting of programs, data procedures, rules, and
associated documentation.
Head
crash
The read/write heads fly across the surface of the disk drive's platters,
traveling on a cushion of air. If the head comes in contact with the platter, a
head crash occurs. Head crashes damage the platter and corrupt the data. Often
the data is rendered inaccessible.
Heads
The read/write head on a hard disk drive is similar to the read/write head on a
tape recorder. Data is stored as changes in magnetic flux on the disk platters.
The read/write heads sweep across the surface, traveling on a cushion of air.
Read/write heads can perform both the reading and writing of data. The drive
will usually have an additional read-only, servo head that is used for disk
positioning.
Hertz
(Hz)
The International System of Units measure of frequency. Hertz was named for
German physicist Heinrich Hertz and was often abbreviated as Hz. One Hertz is
one complete cycle per second. A cycle may relate to light, heat, radio waves,
or other vibrations.
Hexadecimal
A base-16 numeric notation system that specifies addresses in computer memory.
In hexadecimal notation, the decimal numbers 0 through 15 are represented by
the decimal digits 0 through 9 and the characters A through F (A=decimal 10,
B=decimal 11, and so on.).
High-Density
(HD)
The density refers to how tightly data can be recorded on the media. This is
usually used to describe floppy diskettes. Using a magnetic medium that has
much finer (smaller) magnetic particles, more data can be recorded on the
media. HD diskettes require high-density drives.
High
Memory Area (HMA)
The High Memory Area (HMA) is the first 64 KB of Extended Memory and is located
in the address range of 1024 KB to 1088 KB. An Extended Memory (XMS) driver
such as HIMEM.SYS is required for use of the HMA.Only one program may reside in
the HMA.
High-Level
Format
Once the partition(s) have been created on a hard disk, another format is
required before the disk can be used. This is called a high-level format, and
is operating-system dependent. With limited exceptions, a disk formatted under
one operating system cannot be used by another. The steps performed in the
formatting process include creating the boot record and file allocation tables
(or other file tracking system), initializing the disk directory, verifying the
disk surface, and, if needed, transferring the system files.
The boot record contains the bootstrap program that allows the computer to load
(or boot) the operating system from the disk.
For DOS, File Allocation Tables (FATs) are created. These tables keep track of
the sectors assigned to a particular file, as well as the available (empty)
sectors on the disk. Other operating systems have their own equivalent to the
FAT system.
Most operating systems use a hierarchical, tree-like directory system to keep
track of directories, subdirectories, and files on the disk. Formatting
initializes the directory tables by clearing the root (top-most) directory.
During the formatting process, each disk sector is examined to verify that
there are no bad sectors on the disk. Bad sectors are locked out and flagged in
the file allocation table (or equivalent) so the computer will not attempt to
write to these disk areas.
The next step of the formatting process allows the user to have the operating
system's startup files transferred to the disk.
For DOS versions 4.01 and below, the FORMAT process is a destructive one. The
FAT is erased. Even though none of the data on the disk is erased, the data
cannot be recovered without the FAT and directory table information.
DOS 5.00 and newer versions support a safe format. The FAT and directory
information is backed up to a new location on the disk, allowing the user to
unformat the disk, if necessary. Always approach formatting a hard disk as if
it is a destructive procedure. Unformat or safe format utilities do not always
guarantee the ability to recover all of the disk information.
Hub
1. In disk drives, the hub is the central mechanism within the drive that
causes the disk to rotate and keeps it centered during the rotation. On floppy
diskettes, the hub fits into the hole in the center of the diskette to keep it
level and balanced during rotation.
2. In networking, a central connecting point for network wiring.
A value between 0 and 239 that indicates whether a color is more red, yellow,
or blue. Both 0 and 239 are shades of red, with numbers greater than 0 becoming
increasingly yellow and numbers less than 239 becoming increasingly blue. Cyan
has a hue of approximately 120.
I/O
Refers to the sending and receiving of data from the central processing unit
(CPU) to other peripheral devices such as disk drives. The input/output channel
carries out all the transfer of data so as to free up the CPU. The keyboard is
the most common input device, and the monitor is the most common output device.
I/O
address
Space used to access I/O hardware such as I/O adapters, buses, and special
registers used by I/O devices known as control status registers (CSR). I/O
address space is one of two equal parts of primary memory, or addressable
memory. The other equal part is memory address space.
Index
hole
In the past, a 5-1/4-inch floppy drive had to identify the starting position of
a 5-1/4-inch floppy diskette. The drive had to sense when that starting
position reappeared, thus indicating completion of one full rotation of the
diskette. Most drives have a light sensor that reads the index hole rotations
and sees the index hole in the floppy diskette when it lines up with the hole
in the floppy diskette's outer jacket.
A professional ANSI-accredited body of scientists and engineers based in the
U.S. IEEE promotes standardization, and consults to the American National
Standards Institute on matters relating to electrical and electronic
development. The IEEE 802 Standards Committee is the leading official standard
organization for LAN (Local Area Networks).
Integrated
Drive Electronics (IDE)
This is standard interface for a hard disk drive. Controller electronics are
integrated into the drive. The controller connects to a paddleboard that may be
external to, or on, the system board. The paddleboard then interfaces with the
bus to the CPU. An IDE bus can be identified by its 40-pin connector, as opposed
to the 50- pin connector of a SCSI bus.
Interlaced
In monitors, interlacing is often implemented because it is less expensive.
Interlaced monitors allow lower-cost circuitry to be used to display higher
resolutions (scan rate) than it would otherwise be capable of producing.
Interleave
Interleave is a method of arranging disk sectors to compensate for relatively
slow computers. It attempts to minimize the amount of time required to read
consecutive sectors from a single track on the fixed disk. By numbering every
other sector it encounters as though it were the next consecutive sector, the
controller is effectively able to slow the spin rate of the fixed disk drive so
that it can issue a command to read the next consecutively numbered sector.
An interleave ratio that is set to read every other sector as consecutive is
said to run at a 2-to-1 rate. For example, it would start with Sector 1, skip a
sector, number the next sector 2, skip a sector, number the next sector 3, skip
a sector, etc. If set to read every third sector, the interleave is 3-to-1.
Ideally, interleave should be set to the lowest number that the computer, the
disk drive, and the disk controller can support. Virtually all new computers
and disk controllers support 1-to-1 interleave rate.
International
Standards Organization (ISO)
Founded in 1946, the ISO promotes the development of international standards
for the computer, communications, and other fields. ISO members are the
standards organizations of 89 countries. The
Interrupt
Request Lines (IRQ)
Interrupt Request Lines are normally referred to as IRQ lines, and each line
requires a separate IRQ number. Many PC add-in boards and devices require a
unique dedicated IRQ line. Some IRQs are assigned to system devices.
The original IBM PC was an 8-bit system with eight available IRQ lines numbered
0 through 7. These lines support the system timer, keyboard, COM and LPT ports,
and the floppy disk controller.
With the 16-bit IBM AT came eight additional IRQ lines which cascade through
IRQ 2. These IRQ lines support the Real Time Clock, hard disk controller, math
coprocessor, and other devices. Examples of devices that use these IRQ lines
are VGA and network adapters, CD-ROM drives, and SCSI controllers.
Some COM ports share IRQ lines. All odd-numbered COM ports (COM1, COM3, etc.)
share IRQ 4, while all even numbered COM ports share IRQ 3.
Keyboard
The device that allows the user to input data into the computer or to execute
commands. Most keyboards resemble a typewriter. The standard is a 101-key
keyboard.
Kilobit
(Kb)
In computing, it refers to 1024 bits. (A bit is the basic unit for storing data
in primary storage.) Kilobit is used mainly to express the speed of data
transmission.
Kilobits
per second (Kbps)
Thousands of bits per second.
Kilobyte
(KB)
In computing, it refers to 1024 bytes. (A byte is a unit of information
consisting of 8 bits.) Kilobyte is mainly used to express the capacity of
primary storage.
Kilobytes
per second (KBps)
Thousands of bytes per second.
Lamp
A light on a phone device that provides information about the state of a
particular call.
LAN
Adapter and Protocol Support (LAPS)
This is the program that provides LAN adapter and protocol device drivers for
OS/2.
Landscape
A document orientation that has a vertical dimension greater than its
horizontal dimension.
Legacy
Older, non-Plug and Play hardware in use.
Liquid
Crystal Diode (LCD)
LCD monitors are typically used in laptop and notebook systems, as well as
other devices, such as pocket calculators. Their light weight, small size, and
low power consumption make them ideal for these applications. Most PC systems
using LCD monitors now use backlit displays, which allow them to be read in low
light conditions. Color LCD displays are also available.
Logic
Board
The electronic circuit board containing the primary Macintosh components such
as CPU, RAM, Apple ROMs, etc.
LPT
port
The LPT port is also known as a parallel port. It is a connection on the
computer, usually LPT1, where the cable for a parallel printer is connected.
Generally, LPT1 through LPT3 can exist on a personal computer. Special
equipment can be added to extend this capability.
Luminosity
A value between 0 and 240 that indicates the amount of black or white contained
in a particular color. A value of 0 indicates all black. A value of 240
indicates all white.
Mainframe
A legacy computer that is capable of multitasking and other robust operations.
It is generally used as a host for a large number of users.
Master
An instance where the highest privileges reside in a device (usually a
computer) where they have control of other devices or servers.
Math
coprocessor
A specialized chip that supplements the mathematical operations of the CPU or microprocessor.
Older systems had a separate chip for this purpose, while newer systems
incorporate it into the microprocessor.
Media
A generic term for the medium that is used to record data. Media can be a
floppy diskette, a hard disk, or other similar recording surface (an audio tape
for instance).
Megabit
(Mb)
1,048,576 bits.
Megabits
per second (Mbps)
Millions of bits per second (bps).
Megabyte
(MB)
1,048,576 bytes.
Megabytes
per second (MBps)
Millions of bytes per second (Bps).
Megahertz
(MHz)
A million cycles per second. A CPU that operates at 200 Mhz uses a clock
oscillator that runs at 200 million cycles per second.
Memory
A hardware component of a computer system that can store information and
applications for later retrieval. Types of memory are RAM (Random Access
Memory), ROM (Read Only Memory), conventional, expanded, and extended memory.
Menu
1. A displayed list of items from which a user can make a selection.
2. A NetWare menu utility in 3.x that allows for the use of customized menus
created as ASCII text files.
Million
Instructions Per Second (MIPS)
A measure of the speed of execution of a computer's central processsing unit.
Milliseconds
(ms)
A thousandth of a second. Access rates are expressed in milliseconds.
Minicomputer
A legacy computer that is capable of multitasking, but can support fewer users
than a mainframe. An IBM AS/ 400 is a minicomputer.
Modem
An abbreviation for modulator/demodulator. A modem is a peripheral device that
permits a personal computer, microcomputer, or mainframe to receive and
transmit data in digital format across voice-oriented communications links such
as telephone lines.
Monochrome
Monochrome refers to one color (mono=one, chrome=color). Early PC adapters and
monitors were able to send only a single color to be displayed on the black
background of the screen. Although the term "black and white" is
commonly used to describe monochrome, studies have shown that other popular
monochrome colors, like amber and green, actually create less eye strain than white.
While only a single color appears on the black background, many monochrome
monitors do support multiple shades of "gray."
Motherboard
The electronic circuit board containing the primary computer components such as
CPU, RAM, ROMs, etc.
MS-DOS
MS-DOS is Microsoft's version of the DOS operating system.
Multi-Color
Gate Array (MCGA)
Also known as Memory Controller Gate Array, the MCGA graphics adapter was
introduced by IBM to support CGA and some VGA modes.
Multimedia
In computing, multimedia refers to the presentation of information using sound,
graphics, animation, and text.
Multisynch
Multiscanning or multisynch monitors adapt to the incoming horizontal and
vertical frequency signal sent by the computer. By adapting rather than being
fixed at a particular setting, multisynch monitors earn their name and can work
with almost any other video standard. Multisynch monitors were first introduced
as EGA displays.
Multitasking
A mode of operation that provides for the concurrent performance or interleaved
execution of two or more tasks.
Near
Letter Quality (NLQ)
By striking the paper several times to create a character, dot matrix printers
can give the impression of non-dot matrix quality output.
Network
adapter
The card that allows a computer to interface with the network. Also known as a
Network Interface Card (NIC).
Network
board
A circuit board installed in each computer, allowing workstations to
communicate with each other and the network server. Printers that contain their
own network boards can attach directly to the network cabling. NetWare
documentation uses the term network board; it can also be referred to as an
NIC, LAN card, or network adapter card.
Network
Interface Card (NIC)
Workstations communicate with each other and the network server via this
circuit board, which is installed in each computer. It can also be referred to
as an NIC, LAN card, or network card.
Noise
In data transmission, any unwanted electrical signal which interferes with a
communications channel. Noise is often a random transmission of varying
frequency, amplitude, and phase. Such noise may radiate from fluorescent lights
and electric motors, and can also be caused by static, temperature changes,
electric or magnetic fields, or from the sun and the stars.
NuBus
The original expansion bus designed by Apple Computer and introduced in the
Macintosh product line. This has been replaced by the PCI bus.
Null
modem
A device that connects two DTE devices directly by emulating the physical
connections of a DCE device.
Octet
A set of 8 bits or one byte.
Operating
system
The software program that controls all system hardware and provides the user
interface.
Pages
per minute (ppm)
A term used to describe the output speed of printers.
Parallel
interface
A connection between a parallel device, such as a printer, and a computer. The
computer sends multiple bits of information to the device simultaneously. This
is also known as a Centronics interface.
Parallel
ports
In a parallel interface, eight data bits of data are sent at the same time, in
parallel, on eight separate wires. Therefore, parallel transmissions are faster
than serial transmissions.
Parallel ports, also called LPT ports, were originally used to connect line
printers and terminals. Most systems have at least one parallel port, which is
called LPT1.
There are two parallel standards: Bi-Tronics and Centronics (IEEE 1284).
Centronics cables support a higher data rate. The Centronics connector is a
25-pin D-shell connector and is considered the standard.
Printers generally use parallel communications, as do some early notebook PC
network adapters. Devices are available which allow the connection of SCSI
devices to a parallel port.
Parallel
transmission
In computer communications, parallel transmission is the transmission of data
(binary digits) simultaneously (in parallel with each other) using separate
lines. In contrast, serial transmission sends only one bit after the other
using only one communications line.
Parameter
RAM (PRAM)
The permanent memory on a Macintosh system board that stores information such
as system name, LocalTalk address, and hardware configuration. Similar in
function to CMOS Memory used by IBM compatible systems. To reset the PRAM to
factory-set default values, hold down the Command and Option keys while
depressing the "P" and "R" keys when first booting up. The
Mac startup chime will sound multiple times, indicating the PRAM has been
successfully zapped.
Parity
check
A technique used to quickly check the integrity of data received after a
transmission, or from memory. Parity checking can apply to bytes, words, long
words, and other units of information.
PC
Card (PCMCIA)
PCMCIA is a bus definition which defines a hardware interface that supports
very small peripherals, such as credit-card-sized modems, network interface
cards, hard drives, and memory cards.
PC-DOS
PC-DOS is IBM's version of the DOS operating system.
Peripheral
Component Interconnect (PCI)
A high-speed expansion bus technology used by PC and Apple computers.
Pitch
In printing, pitch refers to the number of characters per horizontal inch and
is related to the character point size. Some fonts use a fixed pitch, where the
spacing is the same for each character. Many fonts use a variable or
proportional pitch, where each character has a different width. Overall, controlling
the pitch makes for a better document appearance.
Pixel
A pixel (sometimes called a pel) is an individual picture element. This is the
smallest single element that can be displayed on the screen. Screen resolution
is given in horizontal and vertical pixel counts. The more pixels, the greater
the resolution.
Plasma
display
Plasma video displays operate by exciting a heated gas and tend to get very
warm with extended usage. Formerly, these distinctive orange displays were
often used in laptop and portable systems. Plasma screens allowed for a thin
screen, but the high power consumption made them not suited to battery-powered
systems.
Platters
In hard disks, platters are rigid aluminum disks covered with metal particles
that are magnetized. When read/ write heads sweep across the platter, the
magnetized particles form patterns that represent stored data. Platters are
similar to floppy diskettes, except that there are multiple platters in each
hard disk. Data can be written to both sides of the platter's surface. The term
platters refers specifically to hard (fixed) disk drives. Most drives have at
least four platters; some have as many as ten.
Plug
and Play
The specification for a hardware and software architecture that allows
automatic device identification and configuration.
Point
size
In printing, characters are measured in points. There are 72 points per inch.
The point size refers to the maximum size for any character, measured
top-to-bottom.
Port
1. A memory address that identifies the physical circuit used to transfer
information between a microprocessor and a peripheral.
2. On the Internet, port often refers to a number that is part of a URL,
appearing after a colon (:), immediately after the domain name. Every service
on an Internet server listens on a particular port number on that server. Most
services have standard port numbers. Web servers normally listen on port 80.
Services can also listen on non-standard ports, in which case the port number
must be specified in a URL when accessing the server. You might see a URL of
the form: gopher:// peg.cwis.uci.edu:7000/, which shows a gopher server running
on a non- standard port (the standard gopher port is 70).
3. Port also refers to translating a piece of software from one type of
computer system to another, for example, translating a Windows program to run
on a Macintosh.
Portrait
The orientation setting in which the vertical dimension is longer than the
horizontal dimension.
Power
On Self Test (POST)
When you first start a PC, it will go through a Power On Self Test (POST). The
various parts of the computer are checked in a particular order. If errors are
detected, they are reported to the user.
The first part tested is the basic system. This includes the microprocessor,
bus, and system memory. The extended system is checked next (the system timer,
and, if installed, the ROM BASIC interpreter).
The third group tested is related to the video display. The video signals and
display-adapter memory are tested. If there is more than one display adapter
installed, only the primary adapter is tested.
The memory is tested next. All addressable memory (conventional and extended)
is tested through a write/read test.
The keyboard interface is tested, and the keyboard checked for malfunctioning
(stuck) keys.
Finally, the system will then determine if any disk drives (floppy and/or hard
disks) are installed. If so, they are then tested.
POST errors are reported as audio beeps and numeric error codes. While many
manufacturer's codes are similar, you will want to refer to documentation for
your particular system to identify any error messages.
Power
Supply
A PC's power supply is a device that takes the AC (alternating current)
electric current from the wall and converts it into the DC (direct current)
current required by the computer.
The power supply outputs four discreet voltages: +5 VDC, -5 VDC, +12 VDC, and
-12 VDC. Spikes are smoothed out with capacitors connected across the power
supply leads.
For a list of power supply manufacturers and their home pages, see www.yahoo.com/Business_and_Economy/
Companies/Computers/ Hardware/Components/Power_Supplies.
PowerPC
The microprocessor family jointly developed by Apple, IBM, and Motorola. These
processors are found in Power Macintosh and compatible computers.
Printer
A printer is a peripheral hardware device that produces printed material.
Printer
driver
A program that translates the printed file into the language the printer
understands. A printer cannot be used unless the correct driver is installed.
Printer
fonts
Fonts which are built into the printer. They may also be downloadable soft
fonts.
A communications port located on the rear panel of a computer, designed for the
connection of a printer.
Processor
In a computer the processor, or Central Processing Unit (CPU), this is a
functional unit that interprets and executes instructions. A processor contains
at least an instruction control unit and an arithmetic and logic unit.
Processor-direct
slot
An expansion slot that allows direct connection to the system's CPU(s).
RAM
disk drive
A RAM drive is also known as a virtual drive. A portion of memory used as if it
were a hard disk drive. RAM drives are faster than hard disks because the
memory access time is much faster than the access time of a hard disk. Information
on a RAM drive is lost when the computer is turned off.
Random
Access Memory (RAM)
RAM is the computer's storage area to write, store, and retrieve information
and program instructions so they can be used by the central processing unit.
The contents of RAM are not permanent.
Read-Only
Memory (ROM)
Read-Only Memory is used to store permanent instructions for the computer's
general housekeeping operations. A user can read and use, but not change, the
data stored in the computer's ROM. ROM is stored on a non- volatile memory chip
enabling the information to be retained, even after the computer's power has
been turned off.
The Apple Macintosh ROMs contain a large portion of the operating functionality
in permanent storage on the system board. Macintosh clone vendors must license
these ROMs in order to build Mac-compatible computer systems.
Read/write
heads
In a fixed disk drive, there is one read/write head for every side of each
platter. The read/write heads are said to be gang mounted because they move together
in unison across multiple platters.
Real
mode
The operating mode of the 80286 microprocessor that runs programs designed for
the 8086/8088 microprocessor.
Reboot
The process of restarting a computer system.
Redundant
Array of Independent Disks (RAID)
A Redundant Array of Independent Disks is usually referred to as a RAID system.
The "I" originally stood for Inexpensive, but was changed to
Independent because RAID systems are typically expensive.
A RAID system is composed of multiple hard disks that can either act
independently or emulate one large disk. A RAID disk system allows increased
capacity, speed, and reliability.
RAID was defined in nine levels by to the RAID Advisory Board. Each level
provides a different amount of reliability and fault tolerance. The level
numbers do not indicate that one level is superior to another.
For an online RAID Guide, see www.invincible.com/rguide.htm.
Refresh
Rate
The rate at which a video display monitor redraws screen contents. Higher
refresh rates (72Hz and above) provide better display characteristics than
lower rates (60Hz).
Resolution
In monitors, this refers to the sharpness of the displayed image or text on a
monitor, and is a direct function of the number of pixels in the display area.
Resolution is the number of pixels across one line of the monitor by the number
of lines down the screen (for example, 800x480). The greater the pixel count,
the higher the resolution and the clearer the screen image.
RGB
When referring to the three primary colors used in all color monitors and
adapters, RGB gets it name from these colors: Red, Green, and Blue.
RS-232-C
A low-speed serial interface used to connect data communications equipment
(such as modems and terminals) defined as a standard by the Electronic
Industries Association. All standards recommended by the EIA have an RS prefix.
Saturation
A value between 0 and 240 that indicates the amount of the hue contained in a
particular color. A value of 0 indicates no color. A value of 240 indicates the
greatest saturation of color.
Scan
mode
When a monitor screen is refreshed by the electron gun and beam, there are two
modes of scanning that may be used. With sequential scanning, all lines are
scanned in order from the top left corner, across and then down the screen. This
is sometimes referred to as non-interlaced scanning. With interlaced scanning,
the lines are divided into an odd and an even group. First one (the odd) and
then the other (the even) group is scanned each time the screen is refreshed.
As a result, interlaced scanning takes more time and the image on the display
begins to deteriorate. Because it takes longer for the electron beam to return
to the top corner, after the odd and even scan, to start scanning the odd group
again, flicker is produced as the electron gun refreshes and excites the
phosphor elements on the screen. Non-interlaced scanning is considered
preferable over interlaced.
Scan
rate
Screens must be refreshed several times per second to continue displaying data.
This is called their refresh rate or the frame rate. This rate is expressed