Specifications

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Appendix A Glossary
video adapter An expansion card or chipset
built into a motherboard that provides the capabil-
ity to display text and graphics onscreen. If the
adapter is part of an expansion card, it also
includes the physical connector for the monitor
cable. If the chipset is on the motherboard, the
video connector is on the motherboard as well.
video graphics array See VGA.
video-on-CD or video CD A full-motion digital
video format using MPEG video compression and
incorporating a variety of VCR-like control capabili-
ties. See also White Book.
virtual disk A RAM disk or “phantom disk
drive” in which a section of system memory (usu-
ally RAM) is set aside to hold data, just as though it
were several disk sectors. To DOS, a virtual disk
looks and functions like any other “real” drive.
virtual IRQ PCI IRQs higher than 15 (the end of
the standard IRQ listing). Windows XP Service Pack
1 and later and Windows 2003 Server assign PCI
devices that share hardware IRQs virtual IRQ num-
bers in Device Manager. See also IRQ.
virtual memory A technique by which operat-
ing systems such as 32-bit Windows versions load
more programs and data into memory than they
can hold. Parts of the programs and data are kept
on disk and constantly swapped back and forth
into system memory. The applications’ software
programs are unaware of this setup and act as
though a large amount of memory is available.
virtual real mode A mode available in all Intel
80386-compatible processors. In this mode, mem-
ory addressing is limited to 4,096MB, restricted pro-
tection levels can be set to trap software crashes
and control the system, and individual real-mode
compatible sessions can be set up and maintained
separately from one another.
virtual tape library A disk-based backup
device that emulates a tape library. See also tape
library.
virus A type of resident program designed to
replicate itself. Usually at some later time when the
virus is running, it causes an undesirable action to
take place.
VL-Bus (VESA Local Bus) A standard 32-bit
expansion slot bus specification used in 486 PCs,
the VL-Bus connector was an extension of the ISA
slot; any VL-Bus slot is also an ISA slot. Replaced by
the PCI bus, the VL-Bus slot was used on only a
very few early Pentium systems.
VMM (Virtual Memory Manager) A facility in
Windows enhanced mode that manages the task of
swapping data in and out of 386 and later proces-
sor virtual real-mode memory space for multiple
non-Windows applications running in virtual
real mode.
vmstat A command-line Linux program that can
be used to view server performance and look for
bottlenecks.
voice-coil actuator A device that moves
read/write heads across hard disk platters by mag-
netic interaction between coils of wire and a mag-
net. Functions somewhat like an audio speaker,
from which the name originated. The standard
actuator type on hard drives.
volatile memory Memory that does not hold
data without power. Both Dynamic RAM (the main
RAM in a computer) and Static RAM (used for
cache memory) are considered volatile memory. See
also nonvolatile memory.
volt (V) The unit of measurement of electromo-
tive force. One volt is equal to the force required to
produce a current of 1 ampere through a resistance
of 1 ohm.
voltage reduction technology An Intel
processor technology that enables a processor to
draw the standard voltage from the motherboard
but run the internal processor core at a lower
voltage.
voltage regulator A device that smoothes out
voltage irregularities in the power fed to the
computer.
volume A portion of a disk signified by a single
drive specifier. Under DOS v3.3 and later, a single
hard disk can be partitioned into several volumes,
each with its own logical drive specifier (C:, D:, E:,
and so on).
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