Specifications

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Appendix A Glossary
drives, each with its own specifier. A primary par-
tition can contain only one logical drive; an
extended partition can contain one or more logical
drives. See also extended partition and primary
partition.
logical unit number See LUN.
lossless compression A compression technique
that preserves all the original information in an
image or other data structures. PKZIP and Microsoft
CAB files are popular applications of lossless
compression.
lossless linking A technique used by DVD+RW
drives to enable the DVD+RW video-writing process
to pause and continue as data is available. Lossless
linking enables DVD+RW video media to be read
by standalone DVD video players and DVD-ROM
drives.
lossy compression A compression technique
that achieves optimal data reduction by discarding
redundant and unnecessary information in an
image. MP3, MPEG, and JPEG are popular examples
of lossy compression.
lost clusters Clusters that have been marked
accidentally as “unavailable” in the FAT even
though they don’t belong to any file listed in a
directory. See also cluster.
low-level formatting Formatting that divides
tracks into sectors on the platter surfaces. Places
sector-identifying information before and after each
sector and fills each sector with null data (usually
hex F6). Specifies the sector interleave and marks
defective tracks by placing invalid checksum figures
in each sector on a defective track.
LPT port Line printer port, a common system
abbreviation for a parallel printer port. Common
LPT port numbers range from LPT1 to LPT3.
LPX A semiproprietary motherboard design used
in many Low Profile or Slimline case systems.
Because no formal standard exists, these typically
are not interchangeable between vendors and are
often difficult to find replacement parts for or
upgrade.
luminance Measure of brightness usually used
in specifying monitor brightness.
LUN (logical unit number) A number given to
a device (a logical unit) attached to a SCSI physical
unit and not directly to the SCSI bus. Although as
many as eight logical units can be attached to a
single physical unit, a single logical unit typically is
a built-in part of a single physical unit. A SCSI hard
disk, for example, has a built-in SCSI bus adapter
that is assigned a physical unit number or SCSI ID,
and the controller and drive portions of the hard
disk are assigned a LUN (usually 0). See also PUN.
LZW (Lempel Zev Welch) A lossless compres-
sion scheme used in the GIF and TIFF graphic for-
mats, named after its co-creators, Abraham Lempel,
Jacob Zev, and Terry Welch.
MAC address Short for Media Access Control
address, this is a unique hardware number assigned
to network hardware, such as NICs and routers. The
MAC address assigned to the WAN side of some
broadband Internet routers can be changed to
equal the MAC address of the NIC previously used
to attach to a broadband device, such as a cable
modem.
machine address A hexadecimal (hex) location
in memory.
machine language Hexadecimal program code
a computer can understand and execute. It can be
output from the assembler or compiler.
macro A series of commands in an application
that can be stored and played back on demand.
Many applications from various vendors support
Microsoft Visual Basic for Applications as their
macro language.
macro virus A computer virus that uses a script-
ing language to infect Microsoft Word document
templates or email systems.
magnetic domain A tiny segment of a track
just large enough to hold one of the magnetic flux
reversals that encode data on a disk surface.
magneto-optical recording An erasable opti-
cal disk recording technique that uses a laser beam
to heat pits on the disk surface to the point at
which a magnet can make flux changes.
magneto-resistive A technology originally
developed by IBM and commonly used for the read
element of a read/write head on a high-density
magnetic disk. Based on the principle that the
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