Specifications

Glossary
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resistance to electricity changes in a material when
brought into contact with a magnetic field (in this
case, the read element material and the magnetic
bit). Such drives use a magneto-resistive read sensor
for reading and a standard inductive element for
writing. A magneto-resistive read head is more sen-
sitive to magnetic fields than inductive read heads.
Giant magneto-resistive heads are an improved ver-
sion that store more data in the same space.
mainframe A somewhat vague distinction that
identifies any large computer system normally
capable of supporting many users and programs
simultaneously.
mask A photographic map of the circuits for a
particular layer of a semiconductor chip used in
manufacturing the chip.
master boot record (MBR) On hard disks, a
one-sector-long record that contains the master
boot program as well as the master partition table
containing up to four partition entries. The master
boot program reads the master partition table to
determine which of the four entries is active
(bootable) and then loads the first sector of that
partition, called the volume boot record. The mas-
ter boot program tests the volume boot record for a
55AAh signature at offset 510; if it’s present, pro-
gram execution is transferred to the volume boot
sector, which typically contains a program designed
to load the operating system files. The MBR is
always the first physical sector of the disk, at
Cylinder 0, Head 0, Sector 1. Also called master
boot sector.
math coprocessor A processing chip designed
to quickly handle complex arithmetic computa-
tions involving floating-point arithmetic, offload-
ing these from the main processor. Originally
contained in a separate coprocessor chip, starting
with the 486 family of processors. Intel now has
incorporated the math coprocessor into the main
processors in what is called the floating-point unit.
Maximum Transmission Unit (MTU) The
largest packet that a network can transmit, usually
measured in bytes.
MCA (Micro Channel Architecture)
Developed by IBM for the PS/2 line of computers
and introduced on April 2, 1987. Features include
a 16- or 32-bit bus width and multiple master
control. By allowing several processors to arbitrate
for resources on a single bus, the MCA is optimized
for multitasking, multiprocessor systems. Offers
switchless configuration of adapters, which elimi-
nates one of the biggest headaches of installing
older adapters. MCA systems became obsolete after
the development of the PCI bus.
MCGA (multicolor graphics array) A type of
PC video display circuit introduced by IBM on April
2, 1987, which supports text and graphics. Text is
supported at a maximum resolution of 80×25 char-
acters in 16 colors with a character box of 8×16
pixels. Graphics are supported at a maximum reso-
lution of 320×200 pixels in 256 (from a palette of
262,144) colors or 640×480 pixels in two colors.
The MCGA outputs an analog signal with a hori-
zontal scanning frequency of 31.5KHz and supports
analog color or analog monochrome displays.
MCH (memory controller hub) Intel’s term
for the chip used in its 8xx-series chipsets to con-
nect the processor with high-bandwidth devices
such as memory, video, and the system bus, replac-
ing the North Bridge chip. MCH chips connect
with the I/O controller hub (the 8xx chipsets’
replacement for the South Bridge) through a high-
speed hub interface. See also ICH.
MCI (media control interface) A device-
independent specification for controlling multi-
media devices and files. MCI is a part of the
multimedia extensions and offers a standard inter-
face set of device control commands. MCI com-
mands are used for audio recording and playback
and animation playback. Device types include CD
audio, digital audio tape players, scanners, MIDI
sequencers, videotape players or recorders, and
audio devices that play digitized waveform files.
MDA (monochrome display adapter; also,
MGA [mono graphics adapter]) A type of PC
video display adapter introduced by IBM on August
12, 1981, that supports text only. Text is supported
at a maximum resolution of 80×25 characters in
four colors with a character box of 9×14 pixels.
Colors, in this case, indicate black, white, bright
white, and underlined. Graphics modes are not
supported. The MDA outputs a digital signal with a
horizontal scanning frequency of 18.432KHz and
supports TTL monochrome displays. The IBM MDA
card also includes a parallel printer port.
Appendix A
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