If you don't find the definition you are looking for in this glossary,
try the resources below:
The "Free On-line Dictionary of Computing" is available via the web at:
This dictionary is compiled and maintained by Denis Howe (email@example.com).
A large list of COMPUTER ACRONYMS is defined in the Babel document
accessible via ftp or the web. It is updated 3 times per year, so
you have to request the latest document. It's of the format
YR is the year, i.e. 95
P is the update period i.e. a, b or c:
After May 1, 1995 request BABEL95B.
After Sep 1, 1995 request BABEL95C.
After Jan 1, 1996 request BABEL96A.
ftp://ftp.temple.edu/pub/info/help-net filename as above babelYRP.txt
Babel is compiled and maintained by Irving Kind (firstname.lastname@example.org).
IBM video graphics standard. Supports pixel addressabilities
up to 1024x768 and 256 colours. It is _not_ a superset of VGA.
addressability (pixel addressability)
This refers to the number of pixels that a video controller
can display. It is quoted as the (# horizontal pixels)
by the (# vertical pixels). Common PC pixel addressabilities
320x200, 640x480, 800x600, 1024x768, 1280x1024 & 1600x1200
An array of vertical wires which act in a similar manner as a
shadow mask. Their basic purpose is to permit the correct
electron beam to strike its corresponding colour phosphor only.
This results in crisp pixel definition, and superior colour
brightness than is realized with more traditional designs.
The aperture grille was first used by Sony in their Trinitron
AT bus Advanced Technology (IBM) bus.
The standard PC compatible
peripheral bus to which add-in cards like video, i/o, internal
modems, sound are added. Also called the ISA bus, it runs at
a maximum of 8.33 MHz and has a 16-bit wide data path.
Also called video bandwidth. This is a measure of how much
gross throughput a monitor can handle (in MHz). Bandwidth at
a given pixel addressability is a function of the vertical
refresh rate and monitor timing. see 'How do I calculate the
minimum bandwidth required for a monitor?"
Basic Input Output System. The video BIOS basically tells
the computer how to talk to the video subsystem at boot time.
The video BIOS calls are used by DOS for VGA (and SVGA) modes.
A VGA video operation which copies an array of values to a
rectangular region in video RAM.
This is the number of bits which are available to store colour
information for each pixel displayed. The number of colours
which can be displayed is calculated as two to the exponent
'n', where n is the number of bit planes. i.e. 4 bit equals
16 colours, 8 bit equals 256 colours and 24 bit equals 16.7
million colours. see "How does colour depth (bit planes)
relate to the number of colours?"
Refers to the amount of memory (and therefore number of
simultaneously displayable colours) available to store colour
information for each pixel. see 'bit planes'.
Central Processing Unit. This is the heart and brains of your
computer. It is responsible for executing code, moving data,
calculations, etc. For PC's, this chip is a member of the X86
family including 8088 through 80486, Pentium and Nextgen.
Cathode Ray Tube. Basically the same technology as is in modern
television sets. One or more beams of electrons are focused onto
phosphor, causing it to glow. The phosphor is arranged into an
array (usually close to rectilinear), and the electron beam scans
the phosphor on the screen (similar to how you read text - left
to right and top to bottom), usually 60+ times per second.
Magnetic interference caused by a change in the position of a
monitor in relation to the earth's magnetic field or the
presence of an artificial magnetic field can cause discolour-
ation. To correct this, all colour monitors automatically degauss
at power-on and some also have a manual degaussing button.
This allows the monitor to compensate for the change in the
magnetic field by realigning the electron guns. In some low
cost monitors without degauss buttons it is necessary to leave
the power turned off for at least 20 minutes in order to get
Usually used to indicate the monitor or flat-panel device used as
the primary visual interface.
Usually this is the same as the video card, but some mother-
boards have built-in video, and so don't require an additional
card. The display adapter contains video memory which stores
what is displayed on the computer's monitor. They have a
wide range of features, from a basic frame buffer, to advanced
3D geometric rendering engines.
Technically, this refers to the digital clock signal that
transfers data into the video card's digital to analog converter.
However, it has also become a measure of the maximum gross data
throughput of a monitor. It is measured in MHz, and indirectly
determines the maximum pixel addressability and vertical refresh
rate that a monitor can handle. See "What do those monitor
The distance between a phosphor dot of one phosphor triad to
its closest diagonal neighbour of the same colour on a monitor.
Expressed in mm - i.e. .28 dot pitch means .28 mm between
triads. A smaller value indicates that the phosphor dots
are more closely spaced, and that the resulting image displayed
will be crisper.
see 'stripe pitch'
Dynamic Random Access Memory. The vast majority of system RAM
in modern computers is of this type because of it's low cost.
It is also the most common type of RAM used for video cards.
A specialized type of DRAM called VRAM is also used in higher
end video cards. see "What is the difference between VRAM
Enhanced Graphics Adapter (IBM). Precursor to VGA, all EGA
video modes are supported in VGA, though register compatibility
is not 100%. EGA cards generate a digital signal, and thus
will not drive a modern, analog monitor.
Extended Industry Standard Architecture. This 32-bit bus
standard was created primarily to compete with IBM's MCA bus.
It runs at speeds of up to 8.33 MHz. EISA is a dying standard.
This is a generic term to describe the video hardware in a
computer. Sometimes it is built onto the motherboard, but
usually it is a separate daughter card that fits into one
of the expansion bus slots. The interface between the graphics
controller and the main processor is one of the ISA, EISA, MCA,
VLB or PCI buses. The graphics controller is responsible for
generating the video signal that is sent to the monitor.
Typically a graphics controller contains a graphics coprocessor
which may be a graphics accelerator, video RAM and a RAMDAC.
A secondary processor dedicated to performing video display tasks.
This is a highly misused and now almost meaningless term. For the
purposes of this FAQ, a graphics accelerator is a coprocessor which
is capable of specific graphics operation, independent of the main
system CPU. See the section "How does a video accelerator
work, and will one help me?"
Graphical User Interface. In contrast to text-based interfaces like
DOS or UNIX, GUI's provide more flexibility in terms of colour,
pixel addressability and types of objects that can be displayed.
Examples of GUI's include X-Windows, Microsoft Windows 3.1, OS/2.
A monochrome display adapter which is MDA compatible and
provides graphics modes up to 720x348
see horizontal scan rate
horizontal scan rate (horizontal frequency)
The frequency, expressed in kHz (thousands of times per second),
at which the horizontal deflection circuit operates. This roughly
translates to the number of scanlines displayed on a monitor in
Standard NTSC television signals are interlaced, meaning that
each video frame is divided into two separate fields of
alternating scanlines. The resulting fields are displayed
sequentially, such that what was originally a 30 frame per
second (fps) refresh becomes 60 Hz at half the vertical pixel
addressability. Thin horizontal lines will appear to flicker
on an interlaced display since their effective refresh rate
is only 30 Hz.
Industry Standard Architecture. This is a 16-bit bus standard
which runs at speeds of up to 8.33 MHz. The vast majority of
peripheral add-in cards like modems, sound cards, cdrom
interfaces and other low-bandwidth applications are still ISA
based. VLB and PCI provide higher bandwidth for video and
disk I/O operations.
Look-up Table (LUT)
At higher pixel addressabilites, most graphics controllers can
not simultaneously display as many colours as they are capable
of generating. Because of video card memory limitations, only
a subset of all possible colours can be displayed at one time.
A look-up table stores the mapping information which determines
which subset of all possible colours are available at any given
Monochrome Display Adapter (IBM)
monitor Usually a CRT-based device which directs an electron beam onto
coloured phosphor, causing it to glow. Monitors use the same
basic technology as televisions, but are capable of much higher
pixel addressabilities and resolutions.
The main component of the computer, which contains the CPU
(brain), main memory slots, keyboard connector and expansion bus
slots, among other possible components.
This means that an entire frame is displayed with each screen
refresh. Non-interlaced displays produce a more pleasing screen
image since thin horizontal lines don't flicker with each screen
Original Equipment Manufacturer. Often manufacturers will produce
versions of their products in large quantities for other companies
who either stick their name on them or use them as components for
their systems. OEM products often make it to the retail sales
arena where they are sold at lower prices. An OEM version of a
card _may not_ be equivalent to the retail version.
Peripheral Components Interconnect. This is basically the Pentium
equivalent to the VLB, but with improvements. It is a 64-bit
standard, but is currently only implemented as 32 bits - look
for 64 bit PCI in the future. It performs asynchronously to
the main CPU, meaning that the PCI bus operates at 33 MHz
regardless of the CPU clock. It also allows more than two
devices on the bus, unlike VLB.
This is the smallest dot that can theoretically be resolved on a
colour monitor and consists of three phosphor dots - one each of
red, green and blue. When struck with the electron beam, these
dots glow producing a bright spot on the screen. Practically,
1.2 or more dot triads comprise each pixel on the screen,
although the pixel addressability of some monitors is greater than
their resolution, and in this case a pixel can be smaller than a
dot triad. The result in this case is that small objects may not
This is the smallest addressable display unit available at a
given video addressability. There is no physical thing on a
display that can be called a pixel. Pixels exist only in the
graphics controller bitmap. The screen image in the bitmap is
composed of an array of pixels, arranged in a rectilinear
fashion, with the X axis running horizontally, perpendicular to
the Y axis. A pixel consists of intensity only (in grayscale
monitors) or colour and intensity information (red, green & blue
in colour). While a pixel usually corresponds to a square or
rectangular area, it is displayed as a number of spots on a
CRT. One pixel usually consists of 1.2 or more dot triads.
Flat panel displays are a special case where individual pixels
correspond directly to a picture element on the display.
Random Access Memory. RAM comes in different types, including
DRAM (Dynamic RAM) and VRAM (Video RAM) among others. DRAM is
used as main system memory, while both DRAM and VRAM can be
used on graphics cards.
Random Access Memory Digital-to-Analog Converter. This is part
of the graphics card which converts the digital intensity values
for each of the red, green and blue guns (usually an 8-bit
number) to analog voltages which are sent to the monitor. A
RAMDAC can use its RAM to store look-up table (LUT) information.
When referring to monitors, the number of times that the video
card refreshes the entire screen in one second. Expressed in Hz
The most common misinterpretation of this term is that it is the
same as pixel addressability. In fact, resolution is more
closely related to dot pitch, since it is a limitation of the
monitor rather than of the graphics controller. The resolution
limits how small an object a monitor is able to display.
Red, Green and Blue. By varying the intensity of each of these
colours in a single pixel, the human eye can be fooled into
seeing a wide range of colours. For example, a combination of
red and green appears as yellow, even though no light with a
yellow wavelength is emanating from the screen. This works
because the optical system integrates the photons striking a
region on the retina, and the combined impulses from green
and red sensitive cones are seen as yellow.
The movement of a monitor's electron gun from one side of the
screen to the other results in the appearance of a horizontal
line of varying intensity and colour. Typically, 200 to 1200
horizontal scan lines (lined-up vertically on top of each other)
make-up the image you see on your display.
This is usually an invar mask which acts to block the electron
beam from striking the wrong phosphors in a CRT. The beam
passes through holes in the mask to strike the correct phosphor
while shadowing neighbouring phosphor. i.e. it prevents
a beam intended to strike a red phosphor from striking a
neighbouring green phosphor by causing an electron shadow
over the green dot.
This is similar to dot pitch, but applicable to Sony Trinitron
and similar tubes which use fine vertical wires (aperture
grille) to separate phosphors. Dot stripe is measured as the
distance between the vertical stripes that result. Measures
of dot pitch and dot stripe are _not_ directly comparable.
A common but proprietary picture tube design developed by Sony.
Uses fine vertical wires instead of the more traditional
shadow mask. see "Why does my monitor have 1/2/3 faint
horizontal lines on it?"
vertical refresh rate (vertical scan rate)
The number of fields (on an interlaced display) or frames (on
a non-interlaced display) that are displayed in one second. A
field or frame covers the entire screen area. This is measured
in Hz (cycles per second). It is limited by the monitor and
video card (pixel addressabilities and colour depths). Modern
monitors and video cards provide refresh rates of 60Hz+.
Video Electronics Standards Association. This group has produced
standards for the VLB (Vesa Local Bus), VESA SVGA video modes and
standards for minimum screen refresh rates at various pixel
Video Graphics Array (IBM). Supports pixel addressabilities of
up to 640x480x16. This is the de facto video standard and
consists of a number of video modes. It is still heavily
supported by DOS-based applications and games. see "What is VGA,
and how does it work?"
A dedicated piece of hardware which performs graphics
operations. Also called a display adapter. Consists of
microchips and other electronic components mounted on a
pc-board which connects into a slot (ISA, EISA, MCA, VLB or PCI)
on the motherboard.
Typically monitors are advertised by the diagonal size of the
picture tube in inches. Common sizes are 14", 15", 17", 20"+.
However, the amount of the screen that can be seen is usually
less. For example, most 17" monitors have only a 15.5" diagonal
area used for display, in part because the actual phosphor area
is only about 16" due to the glass thickness. This is partially
due to the fact that the monitor's case covers the edge of the
tube, and partially because monitor manufacturers want to make
you think you're getting a larger display than you are.
see "Size" under "What do those monitor specifications mean?"
VESA Local Bus. This 32 bit bus was originally designed to
provide higher bandwidth for video cards than is available with
the ISA bus. It is optimized for the 486 CPU and can run at
speeds up to 40 MHz with one card on the bus, or up to 33 MHz
with two cards on the bus. The speed of the VLB is dependent,
and runs synchronously with, the main system CPU. Some VLB cards
are not designed to run faster than 33 MHz, though some mother-
boards will clock the bus at up to 50 MHz! VLB 2.0 has been
written, but has not been implemented on many 486 motherboards.
Video Random Access Memory. A specialized type of DRAM, VRAM
is dual-ported, meaning it can be read from and written to at
the same time. see "What is the difference between VRAM and