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640K BARRIER The
Intel 8088 or 8086 microprocessor chips (found in the IBM PC and
XT), were designed to address or manipulate up to 1,024 kilobytes of
random access memory (RAM ). At the time, 640 kilobytes was thought
to be sufficient for DOS and most of its applications. In the early
to mid-1980's, when these systems began to proliferate, most
applications used only 256KB or 512KB of memory (RAM ) and hence,
worked with room to spare. By the late 1980's however, systems were
rarely sold with less than 640KB of memory since applications were
becoming increasingly complex and required more room to operate. The
more recent PC designs still must face the original 640KB barrier
when using DOS , even though they are often required to be
configured with more than 4MB of RAM . There have been various
methods used to circumvent the 640KB DOS barrier . Most require
applications to specifically call for memory above 1MB and
co-operate with different commercially available memory manager
utilities.
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8086 (Eighty-Eighty Six) Released in 1978 by Intel , the 8086 chip
was to be the heart of a computing standard for years to come. It
has 16 bit registers , a 16 bit data bus , a 20 bit address bus ,
and can control up to 1MB of RAM . It was released in the IBM PC/XT,
but not in the original IBM PC due to cost and lack of support.
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8087 (Eighty-Eighty Seven) Released about the same time as the 8088
and 8086 chips , the 8087 is an optional chip (called a math
co-processor ) that works in conjunction with the CPU to speed
floating -point operations. Both the 8088 and the 8086 chips use the
8087 exclusively.
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8088 (Eighty-Eighty Eight) Released in 1979 by Intel , the 8088 chip
is essentially a downgrade from the more powerful, but older, 8086
chip . It has 16-bit registers , a 20-bit address bus , can control
up to 1MB of RAM , but only has an 8 bit data bus . The reason the
8088 was released was that 16-bit support chips were just coming on
the market and with any new technology they were more expensive than
existing technology. The 8088 's 8-bit data bus allowed it to use
the cheaper 8-bit support chips .
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80286 (Eighty-Two-Eighty Six) Released in 1982 by Intel , the 80286
chip has a number of features that make it a large improvement over
its predecessors. It has 16-bit registers , a 16-bit data bus , and
a 24-bit address bus . The larger address bus allowed the 80286 to
address up to 16MB of RAM . The 80286 chip also added a protected
mode of operation. This allowed it to address 1008MB of virtual
memory (See Virtual Memory ). The 80286 could still run in the real
mode of the 8088 and 8086 , thus ensuring "backward compatibility"
with existing software. Starting with an original clock speed of
6MHz, the 80286 chip soon became available in speeds of 8, 10, 12.5,
16, and even 20MHz making it ideal for many business applications.
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80287 (Eighty-Two-Eighty Seven) Released shortly after the 80286
chip , the 80287 chip is a math co-processor used to speed floating
-point operations by applications that specifically called for it.
The 80287 chip was even used in some low-end 80386 chip based
computers before the 80387 co-processor was available. 80386 (DX )
(Eighty-Three-Eighty Six) Released in 1985 by Intel , the 80386 chip
is an enormous improvement over the 80286 chip but retained the
"backward compatibility" to the 8086 chip . It has 32-bit registers
, a 32-bit data bus , and a 32-bit address bus . The 32-bit address
bus allows the 80386 to address up to 4GB of RAM . The 80386 chip
improves on the virtual memory capacity of the 80286 chip raising
the total addressing capacity of physical and virtual memory to
64TB. The 80386 also added a special virtual mode that would allow
it to create an almost unlimited number of virtual -8086s. This
allowed almost any of the shelf program to run in a multitasking
environment. Previously, programs would need to be written
specifically for the multitasking environment. Released with an
original clock speed of 12.5 or 16MHz, the 80386 is now available in
20, 25, 33, and 40MHz speeds . Since the arrival of the 80386SX
chips the original 80386 chip has taken on the name 80386DX .
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80386SX (Eighty-Three-Eighty Six) Released in 1988 by Intel , the
80386SX chip is a less expensive version of the 80386DX . It has
32-bit registers , a 16-bit data bus , a 24-bit address bus , and
address up to 16MB of RAM . The 80386SX is slower when running full
32-bit software, due to it's external data bus of 16-bits , but is
still fully capable of running the same 32-bit software. The virtual
memory capacity is the same as the 80286 , but the 80386SX enables
the programmer to access the virtual memory in a more efficient
manner.
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80387SX (Eighty-Three-Eighty Seven) The 80387SX numeric processing
unit is designed for use with the 80386SX . The NPU provides
hardware support for floating -point arithmetic for programs
specifically written for it.
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80486 (DX ) (Eighty-Four-Eighty Six) The 80486DX is an improvement
over the 80386DX . The 80386 opcodes have been streamlined, an 8K
internal cache is added, and an NPU compatible to the 80387DX is
integrated onto the chip . It has 32-bit registers , a 32-bit data
bus , and a 32-bit address bus . The 32-bit address bus allows the
80486 line to address up to 4GB of physical RAM and 64TB of total
memory (physical plus virtual ).
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80486SX (Eighty-Four-Eighty Six) The 80486SX is basically an 80486DX
without the internal NPU enabled. Everything internally is the same,
the NPU section has just been disabled . It has 32-bit registers , a
32-bit data bus , and a 32-bit address bus . The 32-bit address bus
allows the 80486 line to address up to 4GB of physical RAM and 64TB
of total memory (physical plus virtual ). Many people mistakenly
believe that the 80486SX has a 16-bit data bus , but this is not
true.
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80487SX (Eighty-Four-Eighty Seven) The 80487SX is marketed as an NPU
upgrade for the 80486SX , but is actually a full blown 80486DX .
When this chip is installed in the NPU socket, the 80486SX is
disabled . It has 32 bit registers , a 32 bit data bus , and a 32
bit address bus . The 32-bit address bus allows the 80486 line to
address up to 4GB of physical RAM and 16TB of total memory (physical
plus virtual ). ABIOS (Advanced Basic Input/Output System) Used in
IBM PS/2 machines to support protected mode operation, especially
when running under OS /2.
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ACK (ACKnowlege) Used in telecommunications to verify the receipt of
data.
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ADC (Analog to Digital Converter) Converts an analog signal or wave
form to a digital bit -pattern.
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ADDRESS A number that refers to a location in RAM where information
is stored. An I/O device or a controller card can be mapped to an
address in memory .
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ADF FILE An Adapter Definition File. This file contains the base
address , interrupts, and other pertinent information about a Micro
Channel adapter and is required to configure a device on the Micro
Channel Bus . The file should have the file name extension .ADF.
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ALU (Arithmetic Logic Unit) The part of the CPU that is responsible
for arithmetic and logical functions .
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ANALOG Analog signals are continuously variable and the slightest
change may be significant. Analog circuits are subject to drift,
distortion, and noise, but they are capable of handling complex
signals with relatively simple circuitry. Due to attenuation of the
signal with distance, analog transmissions require amplifiers to
boost, or magnify, the signal. A tape player records and plays an
analog signal, while a CD player reads the information off of the CD
in a digital format then converts it to an analog signal using a
Digital-to-Analog-Converter (DAC).
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ANSI American National Standards Institute. Founded in 1918 as an
organization that proposes, modifies, approves, and publishes
standards for voluntary use in the U.S., ANSI also represents the
U.S. in the International Standards Organization (ISO) and the
International Electrotechnical Commission (IEC). Programming
languages that conform to ANSI standards (such as ANSI C) have met
all the guidelines for syntax rules set by ANSI . For more
information contact ANSI , 1430 Broadway, New York, NY 10018 API
(Application Program Interface) A routine or system call that an
application program uses to access BIOS or DOS services. ASCII
American Standard Code for Information Interchange A standard seven
or eight-bit code that was created in 1965 by Robert W. Bemer and
established to achieve compatibility between various types of data
processing equipment.
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ASCII, pronounced "as-key ," is the common code for microcomputer
equipment, and is rarely found on larger Mainframe systems. The
Standard ASCII Character Set consists of 128 decimal numbers ranging
from zero through 127. The numbers are assigned to letters, numbers,
punctuation marks, and the most common special characters. The
Extended ASCII Character Set also consists of 128 decimal numbers
and ranges from 128 through 255 representing additional special,
mathematical, graphic, and foreign characters.
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ASIC Application Specific Integrated Circuits These Integrated
Circuits are designed for one purpose only. More specifically they
are design to perform a set of tasks and do not work well for
anything else. A CPU would not be a ASIC chip because it is designed
to be used by many different applications (operating systems,
spreadsheets, databases, etc.). An ASIC would be something like the
peripheral controller . This chip is designed to handle the
peripheral ports and nothing else.
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ASSEMBLY LANGUAGE Assembly language is a low-level programming
language. It is a step above machine language in that assembly
language does not use binary numbers, but mnemonic instructions ,
such as LDA x for load register A with x and SHL for shift left.
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ASSOCIATIVE (CACHE) The caching organization where the cache memory
is broken up into banks of equal amounts and then lines . The number
of banks is equal to the number of ways (2-way = 2 banks , 4-way = 4
banks ). The total number of lines is equal to the size of the cache
divided by the size of the data item. Each line represents 2 or 4
data items depending on the type of way-associative caching.(2-way =
2 data items, 4-way = 4 data items). AT (ATtention) Used by Hayes
and Hayes-Compatible modems to signal the beginning of a command
string.
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AWG (American Wire Gauge) An American standard system to measure the
width of wire.
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BASE ADDRESS The location in the host systems memory area or I/O
port areas used to establish communications with a peripheral card .
See also I/O Port.
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BASIC Beginners All-purpose Symbolic Instruction Code This
programming language still maintains a large popularity due to it's
English-like code and ease of use. There have been uncountable
versions of BASIC on many different makes of machines not all of
them compatible with each other. The latest BASIC is Visual Basic by
Microsoft . Visual Basic is a version of BASIC that can be used to
write Microsoft Windows programs.
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BATTERY BACKUP This can mean several things. One meaning is that the
system is plugged into a device that monitors the power coming in
from the wall and provides power for a few minutes if the main power
from the wall goes out. It can also mean the rechargeable battery on
most modern mainboards that supply power to the CMOS RAM when the
system is turned off. The CMOS RAM maintains vital system
information.
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BBS (Bulletin Board System) A computer system running special
software that allows users to "dial-in" using a modem. The program
allows them to post messages, transfer files, send or receive
electronic mail, or even to play on-line games.
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BCD (Binary Coded Decimal) In binary coded decimal, four binary
digits are used to represent the numbers 0 through nine. Each digit
in a decimal number would need its own separate group of four binary
digits, therefore a two digit decimal number would need 8 binary
digits, or 8-bits , a three digit decimal number would need 12
binary digits, or 12-bits .
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BENCHMARK A benchmark is a process or program that can be executed
to measure and compare the performance of one system against
another, or one device against another.
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BINARY The base -2 number system in which only the digits 1 and 0
are used.. The base -2, or binary system, lets us express any
number, if we have enough bits , as a combination of 1's and 0's.
Because these digits can be used to represent two states, on and off
or true and false, they can easily be used to represents two voltage
levels in an electronic device , high and low. The binary system is
at the heart of digital computing. Binary numbers can be written in
four-digit combinations called nibbles, but are generally grouped
into eight digits and called bytes . 16-bit groups are called words,
and 32-bit combinations are called double words.
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BIOS Basic Input/Output System The BIOS is a chip or chips that are
plugged into the main board of a microcomputer that contain machine
language programs. The BIOS is the first "program" run by the
computer. It tells the computer how to configure itself and how to
read the first area on a drive (floppy or hard). The information
that is read off of the first section of the drive is a larger
program that tells the computer how to read the drive in a more
complex manner and where to start reading the operating system.
After the operating system is loaded, the BIOS is responsible for
handling the details of the input and output operations to the
hardware. The BIOS contains routines tailored to the specific
requirements of each peripheral device . As an example, a video BIOS
consists of instructions on ROM that interpret and execute video
requests from applications software. The BIOS executes these
software requests by interacting with the video memory registers ,
the CPU , and the monitor or printer. BIT Binary digIT Computer
words and data are made-up of bits , the smallest unit of
information. A bit can only be represented by a 0 or a 1. This makes
sense to western thinkers because we think in terms of yes and no,
true and false, right and wrong. Most personal computers operate
with 16-bit words (2 bytes ). A bit can be either zero or one,
represented in a circuit by an off or on state, respectively. The
bits are set on or off to store data or to form a code which in turn
sends instructions to the central processing unit. The term 'bit '
was reportedly first used in 1946 by American John Tukey, a leading
statistician and presidential advisor. Two bits is a still a
quarter, a quarter of a byte . A nibble is four bits , eight bits is
equivalent to a byte (or one printed character), two byes is one
word, and two words is a double-word. BNC (British National
Connector) A type of connector used with coaxial cable applications,
such as Local Area Networks and some cable television. BPB (BIOS
Parameter Block ) A table created on the hard drive in the DOS Boot
Record (DBR) that contains information about a disk drive or other
block peripherals. BPS (Bits Per Second) Used as a measurement of
the speed or data transfer between two devices the number of
binary digits that are transmitted every second. BPS is not 'Baud'
rate even though the terms are often confused or interchanged. BOOT
A computer's operating system is initiated with a boot procedure, a
start-up from scratch . The term is a derivative of the phrase "Boot
-Strap" or "Pull yourself up by the Boot -Straps". For personal
computers using DOS , when power is applied the CPU initializes
itself and reads the code stored in a read-only memory chip , called
the ROM BIOS. After some hardware initialization, the boot -loader
program loads one program from disk that occupies the first file
position and usually must be the first entry in the boot disk 's
root directory. That program is usually called IO.SYS. IO.SYS (Or
IBMBIO.COM ) finishes initializing the hardware and loads the Disk
Operating System (DOS ). DOS reads a file called CONFIG.SYS , if it
exists, and carries out the commands it contains, such as modifying
internal DOS tables and/or loading and initializing device drivers.
COMMAND.COM is loaded next which executes each line of the
AUTOEXEC.BAT file, if it exists, and finally displays a prompt
string on the screen waiting for the user to enter a command.
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BOOT PARTITION The primary partition on a hard drive that contains
all of the boot information.
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BUBBLE MEMORY Bubble memory uses a crystalline structure that reacts
to magnetic fields by polarizing itself. Bubble memory retains the
information stored on it even when power is not applied by the use
of permanent magnets. It is very expensive and very slow, and the
most common applications can be found in the military, since the
military requires robust, radiation resistant devices
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BUFFER A temporary storage area used to compensate for a difference
in data speed between two devices .
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BUFFERED WRITE THROUGH (CACHE) (A Cache Write Policy) All memory
writes from the microprocessor are buffered by the cache . The cache
independently updates system memory when the memory bus becomes
available, but does not cache writes . See also Posted Write BUS A
pathway or route through which information is transferred. This can
be a memory bus , an I/O bus , or possibly a data bus .
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BUS MASTER A device that can gain control of a bus without CPU
intervention.
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BYTE A byte is usually defined as 8 bits of data. The largest
decimal number that can be stored in one byte is 255 (all eight bits
set to 1). In 1964, the 8-bit byte became a standard with the
mainframe computer. Half a byte or 4 bits is called a nibble.
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CAD (Computer Aided Drafting/Design) A computer program or system
that assists a drafter or designer with drawing and modeling
problems . CAD programs have gotten more and more complex and now,
as an example, can render (draw) a house, in three dimensions,
allowing the future occupants to "walk-through" the final plans and
make any revisions before any construction has started.
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CAE (Computer Aided Engineering) A computer program or system, like
CAD, that assists an engineer with many very complex calculations
and models. The engineer can design a new water heater or even a new
CPU chip and test the model and the design before any fabrication
has started.
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CAM (Computer Aided Manufacturing) A computer program or system,
often used with CAD and CAE, that enables very complex instructions
to be sent to computerized tools or robots thus increasing the
accuracy of fabrication.
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CACHE (MEMORY) High speed static RAM chips (SRAM) that are used to
temporarily hold portions of main memory . Information in the cache
memory is accessed much faster than that in main memory . A CPU with
a cache spends less time waiting for data to be retrieved and
stored.
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CACHE HIT A read or write cycle in which the information being read
or written is currently stored in the cache .
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CACHE MISS A read or write cycle in which the information being read
or written is not currently stored in the cache .
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CBIOS (Compatibility Basic Input/Output System) Used in IBM PS/2
machines to maintain compatibility with older members in the IBM PC
family.
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CCITT (Consultative Committee International for Telephone and
Telegraph) An international association that sets worldwide
standards for data communications.
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CD-ROM (Compact Disc-Read Only Memory) A transportable digital
mass-storage device that allows access to large quantities of
information. Because it is less volatile and cheaper than other
forms of mass storage, it has gained wide acceptance in the
multi-media arena.
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CGA (Color Graphics Adapter) A display adapter standard, released in
1981 by IBM . It offers a text resolution of 80x25 characters in 16
colors, with one character composed of 8x8 pixels. It supports a
maximum graphics resolution of 320x200 pixels in 4 colors or 640x200
in 2 colors.
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CHIP A chip is an integrated circuit created on a tiny slice of
silicon. A large number of electronic gates, and the paths
connecting them, are formed by very thin films of conductive
material. Different chips have different uses and hence varying
levels of complexity (and price). A CPU chip is much more complex
than a chip used for data storage (memory ). A chip is placed into a
DIP , or other packaging to protect it and make connections. The
entire package is also referred to as a "chip ."
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CISC (Complex Instruction Set Computing) Pronounced "sisk". CISC
refers to CPUs that operate with large sets of instructions . Most
modern personal computers fall into this category, including the IBM
-compatible microcomputers. As computing technology evolved,
instruction sets expanded to include newer instructions that are
complex in nature and sometimes require multiple clock cycles and,
therefore, more time to complete. Computers that operate with system
software based on these instruction sets have been referred to as
complex instruction set computers (CISC). The opposite of the CISC
chips are the RISC (Reduced Instruction Set Computing) computers,
which, as there name implies, have far fewer instructions , but
offer a performance advantage. The newer Intel CPUs use some RISC
ideas in their design.
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CLOCK A computer's clock is an internal timing device . The clock
speed is determined by the frequency of modulation of an oscillator
. Every computer system utilizes an oscillator to regulate the
system clock . The oscillator can be almost any type; an RF
oscillator (allows a wide spectrum of frequencies), a crystal
oscillator (provides only one fixed frequency that must be
manipulated to produce the desired frequency), or even an electrical
circuit designed as an oscillator . A pulse is emitted from the
oscillator that, along with other signals, ensures that the separate
parts of the system do not get out of sync with one another. The
system clock speed is measured in megahertz, MHz.
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CLONE A clone is an imitation or a look-alike. In this context a
clone would be an IBM -compatible computer. Shortly after IBM
introduced the PC, the XT, and the AT, clones appeared on the market
claiming to be IBM -compatible. Some clones were more compatible
than others and some offered improvements on IBM 's design. The low
prices of micro-computers today are due largely to the very
competitive clone market.
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CMOS (Complimentary Metal-Oxide Semiconductor) A type of chip
design that requires little power to operate.
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COBOL (Common Business Oriented Language) A high-level programming
language that is preferred for many applications on mainframe
systems.
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COLD BOOT A computer's operating system is initiated with a boot
procedure, a start-up from scratch . Typically, the cold boot
process consists of a basic hardware check, followed by loading of
the operating system from disk into memory . See also Boot .
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COM (COMmunications port) A port or connection on an IBM PC or
compatible that supports serial communications.
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CON (CONsole) Originally meaning a terminal or teletypewriter, it
now refers to a keyboard and a monitor used for communicating with
the computer. The standard input device . ( See also STDIN)
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CONTIGUOUS Adjacent "linear" storage locations in RAM or a
non-fragmented file disk . Often, as a result of extensive editing
of a disk file, the file becomes broken into parts that reside in
different locations with pointers tying the file together. The file
is then referred to as non-contiguous or fragmented.
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CONTROL-ALT-DELETE On most IBM -compatible computers the keys Ctrl
Alt and Delete Keys pressed simultaneously, make the system restart.
The type of restart is a warm boot . If the computer has "locked-up"
then this sequence of keys may not work. In this case, a cold boot
must be done. This is accomplished by using the reset button or
shutting the power off and on.
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CONVENTIONAL MEMORY The memory space between 0K and 640KB that is
directly addressable by the 8086 and 8088 CPUs and above. DOS and
most DOS applications are designed to use only the lower 640K of
this conventional memory space. The remaining 384K is used for video
RAM , the machine's BIOS, and/or memory mapping for hardware cards .
This area is frequently called DOS memory .
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CPS (Characters Per Second) Used as a measurement of the speed of
data transfer between two devices the number of characters
(usually 7 to 10 bits ) that are transmitted every second. See also
BPS .
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CPU (Central Processing Unit) The CPU is the main component of a
computer system where instructions are fetched, decoded, and
executed. The CPU in a PC consists of a single IC using VLSI (Very
Large Scale Integration) technology. Overall activity of the
computer system is controlled from the CPU .
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CRC (Cyclical Redundancy Check) A form of data quality assurance
used in telecommunications. An algorithm is performed on each block
of data to be transmitted, and the results sent along with the data.
The receiver then performs the same algorithm on the data, compares
it to the results it received and (if valid) sends an ACK
(acknowledge) signal. If there is an inconsistency, the receiver
then sends a NAK (Negative-ACKnowledge) signal and the data block is
transmitted again.
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CRT (Cathode Ray Tube) An imaging device that projects a stream of
parallel lines that, when seen as a whole, form a picture. The
"stream" is actually an electron beam (cathode "rays") inside a
vacuum tube. The beam is focused onto the lens shaped front of the
tube. Televisions and most desktop computer monitors use CRTs.
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CRYSTAL OSCILLATOR A crystal oscillator uses a small piece of
crystal to provide a constant, accurate pulse. An electric current
is applied to the crystal which causes it to vibrate at a fixed
frequency. The vibration modulates the applied voltage at the exact
same frequency. The outgoing signal is now oscillating at a fixed
frequency and can be used as a timing device . A crystal oscillator
contains circuitry to energize the crystal and produce the pulse.
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CUA (Common User Access) Part of IBM 's Systems Application
Architecture (SAA) that sets guidelines for the appearance and
actions of menu bars, dialog boxes, push buttons, and help windows
in a GUI environment.
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CUI (Character User Interface) An entirely ASCII (character) based
operating environment. DOS is a Character User Interface while
Windows is a Graphic User Interface. See also GUI.
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DAC (Digital to Analog Converter) Converts a digital bit pattern to
an analog signal or wave form.
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DAT (Digital Audio Tape) Similar to CDs in the sense that they store
binary (digital) information instead of analog signals. They are
used in the computer field for high quality tape backup systems and
can hold on the average about 2GB of data per tape. The amount of
information that can be stored is dependent on the length of the
tape and the number of tracks per inch.
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DB-9/DB-15/DB-25 Connectors that resemble a "D" shape. The number
after "DB-" indicates the number of pins used in the connector.
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DBR (DOS Boot Record) A sector on a drive that contains a program
which loads the I/O section of DOS (IO.SYS or IBMBIOS.COM ). After
the program contained in the DBR loads the I/O routines , the boot
sequence then uses those I/O routines to complete the loading of the
operating system. It also holds the BPB, (BIOS Parameter Block )
which contains the DOS partition specifications.
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DCA (Document Content Architecture) A specification promoted by IBM
that suggests standards for the structure of document files.
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DCE (Data Communications Equipment) A device that sends and receives
information, usually a modem, over a data line or a telephone
network . See also DTE.
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DDP (Distributed Data Processing) A computer system or network where
the computing power is spread out over several offices or buildings
rather than a single "Computer Room". The DDP System has gained
popularity with the widespread use of PCs and LANs.
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DEVICE DRIVER A program that controls the interface between the
operating system and an external device such as CD-ROM drives ,
scanners, etc. The program is usually loaded by adding the lined
"Device = Program.sys" to the CONFIG.SYS file Only some devices
require a device driver to be loaded.
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DIN (Deutche Industrie Norm (German Industrial Norm)) A committee
that sets German dimensional standards. The keyboard socket on IBM
compatibles is referred to as a 5-pin DIN because it conforms to the
standards set forth by this committee.
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DIP CHIP (Dual In-Line Package ) The Dual In-line Pin (DIP ) is the
traditional computer chip with 8, 14, 24 or even 40 or more metal
legs or prongs, evenly distributed on the left and right sides.
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DIP SWITCH (Dual In-Line Pin Switch) A bank of switches that is
attached to a system board or add-in cards using two rows of pins .
They are typically used for setting hardware options, much like
jumper blocks are, but have no removable parts to lose.
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DIRECT-MAPPED CACHE A cache in which each data item in cache memory
represents that same number data item on each page of main memory .
(e.g. data item 1 in the cache equals data item 1 on page 1, page 2,
page 3, etc. of main memory ).
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DMA (Direct Memory Access) A means of data transfer between a
peripheral or coprocessor and host memory without processor
intervention.
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DOS (Disk Operating System) An interface between user and computer.
The Operating System enables the user to manage system recourses
more effectively through built-in commands. An Operating System that
specializes in one particular resource, like disk drives , is called
DOS - while one specializing in tape drives would be called TOS
(tape operating system). PC-DOS or IBM -DOS , MS-DOS , and DR-DOS
all refer to a brand of DOS by IBM , Microsoft , and Digital
Research respectively.
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DRAM (Dynamic Random Access Memory) In this type of memory each
cell stores information as a charge on a semiconductor , these chips
make up the bulk of memory in a PC. This type of memory needs to be
recharged , or refreshed , many times a second, or else the charges
that represents the data will dissipate. See also Refresh .
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DHRYSTONES A Dhrystone is a unit of measurement used to compare the
performance of one system against another. A Dhrystone Benchmark
would measure items like integer processes per second, enumeration,
and record and pointer manipulation, to name a few. It is most
applicable to measuring speed and throughput of systems programming
applications. The original Dhrystone program was written in Ada in
1984, and the C and Pascal versions are currently more popular.
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DSDD (Double Sided Double Density) Double-Density is the measure of
the distance between the magnetic particles on a floppy diskette .
The magnetic particles are used to record data onto the disk . Under
DOS , a formatted double density floppy disk holds 360KB of data on
a 5.25 inch floppy and 720KB of data on a 3.5 inch floppy . The
double sided prefix means that information is stored on both sides
of the diskette .
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DSHD (Double Sided High Density) High-Density is the measure of the
distance between the magnetic particles on a floppy diskette . The
magnetic particles are used to record data onto the diskette . Under
DOS , a formatted high density floppy disk holds 1.2MB of data on a
5.25 inch floppy and 1.44MB of data on a 3.5 inch floppy . The
double sided prefix means that information is stored on both sides
of the diskette .
--------------------------------------------------------------------------------
DSIR (Dead Skunk In Road) Found mostly in the southern states of
North America, this unfortunate and unpleasant animal can cause many
unknowing travelers to look upon one another with some degree of
disgust while simultaneously rolling up their windows.
--------------------------------------------------------------------------------
DSIR (Dead Squirrel In Road) Although similar to the Dead Skunk In
Road, this animal has a larger habitat and lacks the former's scent
glands. Be forewarned though, this wild beast can be equally
unpleasant.
--------------------------------------------------------------------------------
DTA (Disk Transfer Area) Where outgoing information is gathered
before sending it to the drive , and where incoming information is
gathered before an application program accesses it.
--------------------------------------------------------------------------------
DTE (Data Terminal Equipment) A device , usually a terminal or
computer, that is the origin of the data sent to the DCE or
destination of the data sent by the DCE. See also DCE.
--------------------------------------------------------------------------------
EBBS (Electronic Bulletin Board System) See BBS
--------------------------------------------------------------------------------
EBCDIC (Extended Binary Coded Decimal Interchange Code) Created by
IBM in 1960, this is an eight-bit code similar to ASCII but
generally found on mainframes.
--------------------------------------------------------------------------------
EBDA (Extended BIOS Data Area) In the PS/2 series and some IBM
compatibles, the EBDA is the area in which information about the
hardware, beyond what is kept by the BIOS, is stored The EBDA is
located above 640KB, just after the system's base memory .
--------------------------------------------------------------------------------
EEPROM (Electronically Erasable Programmable Read Only Memory) A
type of ROM that can be erased electronically (as opposed to an
EPROM which must be erased using ultraviolet light). The chip can
then be reprogrammed. When power is removed from the EEPROM it will
still retain its memory .
--------------------------------------------------------------------------------
FIFO (First In, First Out) A strategy that replaces information
based on a first-in, first-out method. The first bit that was
transferred in, will be the first bit of data written out. Used
frequently in data telecommunications. See also LIFO.
--------------------------------------------------------------------------------
FILE SERVER A computer equipped with relatively large amounts of
mass storage that provides file-handling services to a network . The
file server may use various levels of control to regulate access to
common files and applications on the network .
--------------------------------------------------------------------------------
FIRMWARE A program that is in permanent Read-Only Memory on a
peripheral card or device .
--------------------------------------------------------------------------------
HIT RATE (CACHE) Percentage of memory requests that are found in
the cache . The higher the hit rate the better the system
performance .
--------------------------------------------------------------------------------
INTERRUPTA signal that causes the hardware to transfer program
control to some aspect of the OS /BIOS. This signal can be generated
by hardware or software and indicates that a special task needs to
be performed by the CPU . This is how the computer can be told to
stop what it's doing temporarily and handle another task such as
servicing a peripheral . I/O PORT In addition to peripherals
residing at certain memory locations, they can also use I/O ports to
communicate with the system and input and output data. These are
distinct from system memory and also have their own addresses . See
also Base Address .
--------------------------------------------------------------------------------
IRQ Interrupt Request A method used by NICs and other peripheral
cards to inform the CPU that it is in need of servicing. When an IRQ
is triggered on a device , the CPU stops what its doing to service
it. Each peripheral card installed into a system usually must have a
unique IRQ setting.
--------------------------------------------------------------------------------
LAN Local Area Network A communications system that spans a limited
geographic area, and which provides communication among various
computer devices .
--------------------------------------------------------------------------------
LED (Light Emitting Diode) An electrical component that only allows
current to flow in one direction. When the polarity of the current
is applied properly to the diode (negative to positive and positive
to negative), this type of diode will glow. LEDs are commonly use to
indicate the status of something (e.g. power on).
--------------------------------------------------------------------------------
LIF (Low Insertion Force) A type of socket requiring minimal force
to insert a chip .
--------------------------------------------------------------------------------
LIFO (Last In First Out) A strategy that replaces information based
on a last-in, first-out method. The last bit that was transferred
in, will be the first bit of data written out. Used frequently in
data telecommunications. ( See also FIFO)
--------------------------------------------------------------------------------
LIM (Lotus /Intel /Microsoft) The extended memory system (EMS )
developed by Lotus , Intel , and Microsoft .
--------------------------------------------------------------------------------
LOW LEVEL See Low-Level Formatting.
--------------------------------------------------------------------------------
LOW-LEVEL FORMATTING The first step in preparing a drive to store
information after physical installation is complete. The process
sets up the "handshake" between the drive and the controller . LPT
(Line PrinTer) A parallel port on a PC-compatible computer.
--------------------------------------------------------------------------------
LSB (Least Significant Bit) The bit to the far right of a binary
number. This bit has the smallest value of all the bits in the
number.
--------------------------------------------------------------------------------
LSI (Large Scale Integration) Chips containing approximately more
than 100, but less than 20,000 transistors , internally.
--------------------------------------------------------------------------------
MAIN BOARD The printed circuit board where most major components of
a microcomputer system are located. The main board provides
connections for the CPU , NPU , memory , cache , and expansion cards
. In certain cases, some or all the aforementioned components may
reside on an expansion card , or module. In this case the board
might be called a backplane.
--------------------------------------------------------------------------------
MAU (Multistation Access Unit) The central hardware device on a
network that transmits signals onto the network . A MAU usually has
up to eight ports for devices (work stations) and two ports for
connecting to other MAUs. A MAU can isolate a problem device (work
station or another MAU) to prevent the entire network from failing.
(Also known as a Hub.)
--------------------------------------------------------------------------------
MBR (Master Boot Record) A program loaded by the BIOS boot routine
containing the hard drives partition table. The MBR is used to
locate and load the operating system boot sector.
--------------------------------------------------------------------------------
Mbps (Megabits per second) A term used to describe the number of
megabits of data a network card or other device can send or receive
in a second.
--------------------------------------------------------------------------------
MCA (Micro Channel Architecture) proprietary IBM design. The MCA
The type of system design used in the IBM PS/2 line of computers.
This is a bus is capable of handling a bus width of up to 32 bits .
The multiple master control allows several processors to arbitrate
for resources on a single bus . MCA is optimal for multitasking on
multiprocessor systems.
--------------------------------------------------------------------------------
MCB (Memory Control Block) A 16 byte region preceding each block of
memory controlled by DOS , used to identify the size and holder of
the next block of memory .
--------------------------------------------------------------------------------
MCGA (MultiColor Graphics Array) An IBM video display comparable to
VGA .
--------------------------------------------------------------------------------
MDA (Monochrome Display Adapter) The simplest display adapter
available utilizing a single color to display characters. The most
common used types were amber or sharp green and black colored
screens.
--------------------------------------------------------------------------------
MEMORY A storage facility where data is kept electronically. MFLOPS
(Millions of FLoating -point Operations Per Second) A unit of speed
used to describe the processing speed of NPU 's.
--------------------------------------------------------------------------------
MGA (Monochrome Graphics Adapter) A single-colored display adapter
utilizing bit mapping to allow graphic display capabilities, as well
as MDA type text.
--------------------------------------------------------------------------------
MIPS (Million Instructions Per Second) The number of
machine-language instructions , in millions, a computer can execute
in a second. MIPS vary from computer to computer and should only be
used as a general measurement of performance .
--------------------------------------------------------------------------------
MODEM (MOdulator DEModulator) A device allowing computers to
communicate (transmit and receive data) over a telephone.
--------------------------------------------------------------------------------
MOTHER BOARD A term meaning "main board." See also Main Board.
--------------------------------------------------------------------------------
MOS (Metal Oxide Semiconductor) A technology used in fabricating
integrated circuits.
--------------------------------------------------------------------------------
MPU (Multi or Micro Processor Unit) An integrated circuit that reads
coded instructions for execution. See also CPU .
--------------------------------------------------------------------------------
MSB (Most Significant Bit) The bit to the far left of a binary
number, with the greatest value. See also LSB .
--------------------------------------------------------------------------------
MS-DOS (MicroSoft -Disk Operating System) A disk operating system
created by the Microsoft Corporation. See also DOS .
--------------------------------------------------------------------------------
MSI (Medium Scale Integration) Chips containing approximately more
than 10, but less than 500 transistors , internally.
--------------------------------------------------------------------------------
MTBF (Mean Time Between Failures) A statistically derived amount of
time a device will probably run before a hardware failure occurs. MTBF varies from system to system and should not be relied upon as
an accurate unit measure between different computers, even if they
have the same MTBF rating.
--------------------------------------------------------------------------------
MTTR (Mean Time To Repair) An amount of time a technician will
probably take to repair a specific device .
--------------------------------------------------------------------------------
MUX (MUltipleXer) When registers are grouped in blocks , a specific
device is needed to access individual registers . A mutiplexer is
such a device .
--------------------------------------------------------------------------------
NETWARE A network operating system developed by Novell. NETWORK A
collection of connected computers that can communicate and share
peripherals.
--------------------------------------------------------------------------------
NIC (Network Interface Card) A peripheral card that allows the
computer to communicate with devices and other computers on a
network .
--------------------------------------------------------------------------------
NMI (Non-Maskable Interrupt) An interrupt that cannot be masked or
turned off by software during normal operation. An NMI is usually
used to make the microprocessor aware of memory parity errors.
--------------------------------------------------------------------------------
NMOS (Negative-channel Metal-oxide Semiconductor) A design used in
the manufacture of ICs. See also CMOS . NODE Any terminal,
workstation, or other communications terminal on a network .
--------------------------------------------------------------------------------
NPU (Numeric Processing Unit) A chip that works with the CPU to
speed up floating point arithmetic and high-precision integer
calculations. See also coprocessor.
--------------------------------------------------------------------------------
OCR (Optical Character Reader or Optical Character Recognition)
Information processing technology that reads written or typed alphanumerics into ASCII files in a computer. Usually a scanner is
used with OCR software to make the conversion.
--------------------------------------------------------------------------------
OEM (Original Equipment Manufacturer) A manufacturer that sells its
products to a reseller. This term has been badly warped by the
industry and is also now used to mean the company that sells the
equipment to the end-user or another reseller.
--------------------------------------------------------------------------------
OS (Operating System) An operating system is the master program that
defines the environment in which other programs will run. A program
must be written specifically for that operating system. DOS , OS /2,
and UNIX are operating systems. Microsoft Windows is not a full
operating system because it runs on top of DOS , but it does contain
OS code it could be called an OS extension.
--------------------------------------------------------------------------------
OSC (OSCillator) An electrical component that continuously
generates an electrical pulse at a set frequency. These pulses are
used to synchronize the operations of a computer.
--------------------------------------------------------------------------------
OSI (Open System Interconnection) Guidelines that enable the design
and implementation of a network that allows equipment from different
venders to communicate with each other.
--------------------------------------------------------------------------------
PAL (Programmable Array Logic) A small computer logic chip that can
only be programmed once.
--------------------------------------------------------------------------------
PARITY CHECKING A simple form of error detection. In a PC every byte
of memory is assigned a parity bit . The parity bit is used as a
checksum . For a further explanation of parity checking.
--------------------------------------------------------------------------------
PC-DOS (Personal Computer-Disk Operating System) A disk operating
system created by Microsoft Corporation for the IBM Personal
Computer. It is essentially the same as MS-DOS .
--------------------------------------------------------------------------------
PCL (Printer Control Language) A printer language written for
Hewlett Packard and compatible laser printers. See also PS.
--------------------------------------------------------------------------------
PCMCIA (Personal Computer Memory Card International Association) A
trade and standard setting organization that's purpose is to define
and promote the PC memory card .
--------------------------------------------------------------------------------
PEL (Printing ELement) IBM 's term for a printed pixel, the smallest
region on a page that can be printed.
--------------------------------------------------------------------------------
PERIPHERAL A device attached to a computer to perform an
input/output function such as network cards , modems, and printers.
--------------------------------------------------------------------------------
PGA (Pin Grid Array) A thin, flat ceramic chip package approximately
an inch square that attaches to the circuit board via the pin leads
on the chip 's underside.
--------------------------------------------------------------------------------
PGA (Professional Graphics Adapter) A limited -production,
high-resolution graphics card for the IBM XT and AT systems
(released before VGA ).
--------------------------------------------------------------------------------
PIF (Program Information File) Defines the parameters of a
non-Microsoft Windows program that allows it to run in Microsoft
Windows .
--------------------------------------------------------------------------------
PIO (Programmed Input/Output) A means of data transfer that requires
the use of the host processor . This is different from DMA . See
also DMA , and I/O Port.
--------------------------------------------------------------------------------
PLCC (Plastic Leaded Chip Carriers) A thin, flat chip carrier
(package ) that is constructed of plastic instead of ceramic. It is
surrounded by "J" leads and fits flush into a plastic socket.
--------------------------------------------------------------------------------
PMOS (Positive-Channel Metal-Oxide Semiconductor) A type of design
used in the manufacture of ICs. See also CMOS , and NMOS. PORT
Connectors allowing a device to attach to another one.
--------------------------------------------------------------------------------
POST (Power -On Self Test) When the microcomputer system is powered
on or cold booted , the BIOS initiates a series of hardware tests,
called the POST , to insure that the system is functioning properly.
The diagnostic routines check the primary system board components ,
memory and interrupt controllers, expansion cards that have on-board
ROM routines are initialized, the video controller card is tested
and initialized, all RAM addresses are tested, and finally the
keyboard and disk drive . The POST usually ends with a single beep
and if all has gone well, the system will attempt to boot from
either a floppy or hard drive .
--------------------------------------------------------------------------------
POST CODE The code sent back to the test port, for use by the
technician in diagnosing system problems .
--------------------------------------------------------------------------------
PS (PostScript language) A page-description language developed by
Adobe Systems for converting and moving data to a laser printed
page. Using PostScript, the laser printer mathematically interprets
a full page of shapes and curves, instead of dot-by-dot
(pixel-by-pixel).
--------------------------------------------------------------------------------
PROTOCOL A set of procedures or conventions used between different
types of computer equipment to facilitate communications.
--------------------------------------------------------------------------------
PROM (Programmable Read Only Memory) A ROM chip that is
programmable once by a special device .
--------------------------------------------------------------------------------
PSP (Program Segment Prefix) A 256-byte header that DOS creates for
every program it runs, containing program management information.
--------------------------------------------------------------------------------
QFP (Quad Flat Pack) A popular method of packaging ICs for surface
mounting.
--------------------------------------------------------------------------------
RAM (Random Access Memory) This type of memory is temporary and the
data stored in it is lost when power is turned off or the system is
rebooted. See also DRAM and SRAM.
--------------------------------------------------------------------------------
RBBS (Remote Bulletin Board System) See BBS.
--------------------------------------------------------------------------------
REFRESH This is when the computer recharges the DRAM . DRAM chips
must be refreshed tens of thousands of times each second to prevent
the charges that represent the information from dissipating.
--------------------------------------------------------------------------------
RFI (Radio Frequency Interference) This is interference that is
transmitted and sometimes received by your computer within the radio
spectrum.
--------------------------------------------------------------------------------
RFT (Revisable Format Text) A DCA document file standard, that
includes enough format information to allow editing file contents.
--------------------------------------------------------------------------------
RFU (Reserved for Future Use) In many computer systems today a
number of jumpers , switches, or other components are sometimes
deemed "RFU", these are reserved for operations or functions that
may be implemented at a later time.
--------------------------------------------------------------------------------
RISC (Reduced Instruction Set Computers) Computers having CPUs that
respond to a relatively simple set of instructions that can be
executed in a single clock cycle , unlike CISC computers which may
take several clock cycles per instruction and use a much more
complex set of microcode. See also CISC.
--------------------------------------------------------------------------------
ROM (Read Only Memory) This type of memory is permanent and does
not lose the information stored in it when power fails or the system
is rebooted. As the name says, ROM can only be read, you can not
write to it. See also EPROM, EEPROM, and PROM.
--------------------------------------------------------------------------------
RWRAM (Read Write Random Access Memory) The proper name for what
has been commonly shortened to RAM .
--------------------------------------------------------------------------------
SAA (Systems Application Architecture) A set of IBM guidelines for
creating functionally consistent applications across a wide variety
of computers, from PCs to mainframes.
--------------------------------------------------------------------------------
SBC (Single Board (micro) Computer) A computer that combines a
microprocessor , a clock , memory , data buses and address buses on
a single printed circuit board.
--------------------------------------------------------------------------------
SCSI (Small Computer Systems Interface) A standard, using a 50 pin
connector, that allows up to 64 devices (usually only 8 are used or
supported), including the host, to be connected in a daisy chain
configuration .
--------------------------------------------------------------------------------
SDLC (Synchronous Data Link Control) A protocol developed by IBM to
define operations at a link-level of communications, like the format
of data frames exchanged between modems over a phone line .
--------------------------------------------------------------------------------
SFT (System File Table) Where DOS keeps track of all open files.
--------------------------------------------------------------------------------
SIMM (Single In-line Memory Module) A small printed circuit board
with a card edge connector populated with three to nine DRAM chips
(nine being the most common on eight-bit SIMMs eight chips for
data and one chip for parity ) providing system memory in blocks of
64KB, 256KB, 1MB, 4MB, and 16MB. Thirty-six bit SIMMs look similar
to eight-bit SIMMs , but provide system memory in blocks of 256KB,
1MB, 4MB, 16MB. Double density 36-bit SIMMs provide system memory in
blocks of 512KB or 2MB. SIPP (Single In-line Pin Package ) A small
printed circuit board with a single row of 30 pins populated with
nine DRAM chips (eight chips for data and one chip for parity )
providing system memory in blocks of 64KB, 256KB, 1MB, 4MB. SIPPs
are older than SIMMs and are not supported on newer equipment.
--------------------------------------------------------------------------------
SMD (Surface Mount Device) Components that are specifically
designed to be surface mounted. They differ from DIPs in that holes
do not need to be drilled into the printed circuit board to mount
them.
--------------------------------------------------------------------------------
SMT (Surface Mount Technology) A newer method of attaching ICs and
other components to the surface of both sides of a printed circuit
board.
--------------------------------------------------------------------------------
SRAM (Static Random Access Memory) A type of RAM that holds its
data as long as power is being applied to it. SRAM is much faster
and more expensive than DRAM . SRAM is usually implemented as fast
CACHE memory in PCs.
--------------------------------------------------------------------------------
SPT (Sectors Per Track) A term used to define the number of sectors
per track on a hard drive .
--------------------------------------------------------------------------------
SQL (Structured Query Language) A standard relational database
language.
--------------------------------------------------------------------------------
SSI (Small Scale Integration) Chips containing approximately more
than 1 but less than 10 transistors internally.
--------------------------------------------------------------------------------
TAG RAM Since the cache holds copies of data or instructions that
are in main system memory , it is important to know when a copy is
available in the cache . As information is copied into the Data
Cache RAM , its main system memory address or some part of the
address is also stored in the Tag RAM . How much of the address is
stored in the Tag RAM depends on the type of caching architecture
used. The Tag RAM also contains additional status bits used by the
Cache Management Logic, and each directory entry is called a "tag ."
--------------------------------------------------------------------------------
TLB (Translation Look-aside Buffer) A cache chip used for page table
entries. TLBs are implemented in 80386 and 80486 based systems to
speed up the calculations of linear addresses .
--------------------------------------------------------------------------------
TOS (Tape Operating System) An operating system specifically
designed for systems using tape drives . See also DOS .
--------------------------------------------------------------------------------
TPA (Transient Program Area) A region in memory reserved for user
programs running under DOS
--------------------------------------------------------------------------------
TSOP (Thin Small-Outline Package) A popular design used in surface
mount technology.
--------------------------------------------------------------------------------
TSR (Terminate and Stay Resident) A program that remains in memory
after being terminated. Some TSR programs can be reactivated even
during the operations of other programs.
--------------------------------------------------------------------------------
TSS (Task State Segment) A segment of memory where the processor
stores a snapshot of the PCs context each time a specific task is
suspended.
--------------------------------------------------------------------------------
TTL (Transistor -Transistor Logic) A type of electronic design used
to create logic on a silicon chip , which uses only transistors .
--------------------------------------------------------------------------------
UAE (Unrecoverable Application Error) Microsoft Windows specific.
This is an error that occurs in protected mode when a program
attempts a prohibited memory access or other illegal operation,
which Windows intercepts and reports as an UAE.
--------------------------------------------------------------------------------
UART (Universal Asynchronous Receiver/Transmitter) A device that
converts parallel data into serial form for transmission along a
serial interface and vice versa.
--------------------------------------------------------------------------------
UMB (Upper Memory Block) A region of upper memory space in which
some RAM has been placed and then allocated, under the control of a
memory manager; for use by one or more programs.
--------------------------------------------------------------------------------
UV-EPROM (UltraViolet light Erasable Programmable Read Only Memory)
An EPROM that can have its contents erased by the use of an
extremely bright ultraviolet light. Usually simply called an EPROM.
See also ROM and EEPROM.
--------------------------------------------------------------------------------
UNIX UNIX is an operating system developed by AT&T at Bell
Laboratories by a team of programmers lead by Ken Thompson and
Dennis M. Ritchie. Since the UNIX operating system is easy to use,
its design concept had a great influence on other operating systems
for microcomputers. UNIX is widely used on a variety of computers,
from mainframes to micros. It is a powerful multitasking, multi-user
system with many high-level utility programs. Because of its
superior capabilities as a program development system, UNIX is
expected to continue to grow in popularity.
--------------------------------------------------------------------------------
VAR (Value Added Reseller) A company that resells another company's
products and either improves on it in some way, for instance by
adding something, or provides a service with the product.
--------------------------------------------------------------------------------
VAX A line of minicomputers from Digital Equipment Corp.
--------------------------------------------------------------------------------
VGA (Video Graphics Array) An improvement over the EGA format. VGA
uses analog instead of digital signals, this allows an almost
unlimited number of colors to be displayed. The actual number of
colors you can display is limited by the program you are running and
the number of colors the video card can display.
--------------------------------------------------------------------------------
VLSI (Very Large Scale Integration) Chips that contain approximately
more than 20,000, but less than 300,000, transistors internally.
--------------------------------------------------------------------------------
VME (Virtual Machine Environment) An application program that
emulates an independent 8086 CPU .
--------------------------------------------------------------------------------
VRAM (Video Random Access Memory) A dual-ported memory chip that is
used on some video adapters. The chip allows the CPU to load data
through the chip 's parallel port while the video controller is
reading pixel information through the chip 's serial port.
--------------------------------------------------------------------------------
VRM (Voice Recognition Module) A module that plugs into your
computer that recognizes voice as an input source. VRMs are still
being improved, but the better ones can do fairly well.
--------------------------------------------------------------------------------
WORM (Write Once Read Many) An optical storage device that can save
more than 200MB of data. Each area of the disk can only be written
to once.
--------------------------------------------------------------------------------
WS (Wait States) These are pause cycles . When the processor must
wait one or more clock cycles for the memory to respond it is called
a wait state . These pauses in the system's operations allow the CPU
to synchronize with lower-cost slower memory .
--------------------------------------------------------------------------------
WYSIWYG (What You See Is What You Get) A feature of some application
programs where screen displays appear the same as a printed hard
copy.
--------------------------------------------------------------------------------
XENIX A UNIX based multi-user, multi-tasking, operating system for
the PC environment.
--------------------------------------------------------------------------------
XGA (eXtended Graphics Array) A new IBM graphics standard that
offers better resolution than VGA and uses an on-board video
co-processor to make the video subsystem faster.
--------------------------------------------------------------------------------
XMM (eXtended Memory Manager) Manages extended memory according to
the XMS standards. See also XMS .
--------------------------------------------------------------------------------
XMS (eXtended Memory Specification) This defines how to communicate
with a memory manager that controls access to upper, high, and
extended memories .
--------------------------------------------------------------------------------
X-ON/X-OFF (Transmitter ON/Transmitter OFF) Standard ASCII control
characters used to tell an intelligent device to stop or resume
transmitting data.
--------------------------------------------------------------------------------
ZBR (Zone Bit Recording) A media optimization technique where the
number of sector per tracks is dependent upon the cylinder
circumference; i.e., tracks on the outside cylinders have more
sectors per track than the outside cylinders . The ZBR format is
only done at the factory.
--------------------------------------------------------------------------------
ZERO WAIT -STATE This is when no wait -states are required. Many
systems implement a cache system that allows them to run at 0 Wait
States. See also WS.
--------------------------------------------------------------------------------
ZIF (Zero Insertion Force) A type of chip socket that requires
virtually no insertion force for the installation of a chip .
--------------------------------------------------------------------------------
ZIPP (Zig-zag In-line Pin Package) A chip that has all it's leads
on one edge in a zigzag pattern and mounts vertically to the printed
circuit board.
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