Glossary of Acronyms

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MAU - Multistation Access Unit. The hub of the Token Ring network architecture and can connect as many as eight nodes. Often referred to by the IBM specification of 8228.

MBR - Master Boot Record. A record created during the boot process after the first harddisk is identified by the ROM initialization code. The first 446 bytes of this record are a program that is to be executed. The rest of the record is a two byte header and four 16 byte table entries to define up to four partitions. These can be four Primary partitions or three Primary Partitions and one extended partition contain Logical Volumes. The MBR program reads the first 512 byte sector from the Primary Partition into storage. It then jumps to the program in that sector.

The Master Boot Record, also known as the a partition table, is the sector located at cylinder 0, head 0, sector 1, or LBA 0. This sector is created by an FDISK utility program. The MBR may be the only partition table sector, or the MBR may be the first of multiple partition table sectors that form a linked list. A partition table entry can describe the starting and ending sector addresses of a partition (also known as a logical volume or a logical drive) in both L-CHS and LBA form. Partition table entries use the L-CHS returned by INT 13H AH=08H. Older FDISK programs may not compute valid LBA values.

MCA - Micro Channel Architecture. A type of computer bus design or architecture introduced by IBM in 1987. Largely obsolete today, the MCA bus ran at 10 MHz. A proprietary standard established by IBM to take over from ISA, and therefore incompatible with anything else. It comes in two versions, 16- and 32-bit and, in practical terms, is capable of transferring around 20 Mbps. 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 eliminates one of the biggest headaches of installing older adapters.

MCE - Machine Check Detection. A function supplied the Intel Pentium processor that executes error detection of internal devices and the external bus interface. Exceptions are generated for a variety of conditions when the MCE bit in CR4 is set.

MCD - Multimedia Cartridge Drive.

MCGA - MultiColor Graphics Array. A type of PC video display circuit introduced by IBM on April 2, 1987, that supports text and graphics. Text is supported at a maximum resolution of 8Ox25 characters in 16 colors with a character box of 8xl6 pixels. Graphics is supported at a maximum resolution of 32Ox2OO pixels in 256 (from a palette of 262,144) colors or 64Ox480 pixels in 2 colors. The MCGA outputs an analog signal with a horizontal scanning frequency of 31.SKHz, and supports analog color or analog monochrome displays.

MCM - Multichip Module. A single IC package that contains two or more individual die.

MDA - Monochrome Display 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 80x25 characters in four colors with a character box of 9xl4 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 18.432 KHz, and supports TTL monochrome displays. The IBM MDA also included a parallel printer port.

MFM - Modified Frequency Modulation. Common technique used to encode the magnetic fluxes recorded on a drive into data. Still used on floppy drives and most XT and AT systems. Notice that most drive types supported in CMOS have 17 sectors per track. This is the standard density for MFM encoding.  encoding data as a series of magnetic flux reversals on disk or tape, commonly knownas double-density recording. In contrast to FM, modified frequency modulation omits all clock pulses except those between pairs ofzero bits. See also FM and RLL.

MHz An abbreviation for megahertz, a unit of measurement indicating the frequency of one million cycles per second. One hertz (Hz) is equal to one cycle per second. Named after Heinrich R. Hertz, a German physicist who first detected electromagnetic waves in 1883.

MIDI - Musical Instrument Digital Interface. An interface and file format standard for connecting a musical instrument to a microcomputer and storing musical instrument data. Multiple musical instruments can be daisy-chained and played simultaneously with the help of the computer and related software. The various operations of the instruments can be captured saved, edited, and played back. A MIDI file contains note information, timing (how long a note is held), volume, and instrument type for as many as 16 channels. Sequencer programs are used to control MIDI functions such as recording, playback, and editing. MIDI files store only note instructions and not actual sound data.

MI/MIC - Mode Indicate/Mode Indicate Common. also called forced or manual originate. Provided for installations in which equipment other than the modem does the dialing. In such installations, the modem operates in dumb mode (no auto-dial capability), yet must go off-hook in originate mode to connect with answering modems.

MIPS - Million Instructions Per Second. Refers to the average number of machine-language instructions a computer can perform or execute in one second. Because different processors can perform different functions in a single instruction, MIPS should be used only as a general measure of performance among different types of computers.

MMU - Memory Management Unit. A chip or circuit that translates virtual memory addresses to physical addresses and may implement memory protection.

MMX - Multi Media Extension. A set of multimedia oriented x86 instructions that Intel is adding to versions of the Pentium and other processors. SIMD (Single Instruction Multiple Data) is the basis for Intel's new MMX technology that allows many pieces of information to be processed with a single instruction, providing parallelism that greatly increases performance.

MO - Magneto-Optical. MO drives utilize both magnetic and optical storage properties. MO technology is erasable and recordable, as opposed to CD-ROM (Read-Only) and WORM (Write-Once) drives. MO uses laser and magnetic field technology to record and erase data. The laser is used to heat an area on the disk, which can then be recorded magnetically. MO drives are most commonly used in removable storage applications.

MOS - Metal-Oxide Semiconductor. Refers to the three layers used in forming the gate structure of a field-effect transistor (FET). MOS circuits offer low-power dissipation and enable Transistors to be jammed close together before a critical heat problem arises. PMOS, the oldest ,type of MOS circuit, is a silicon-gate P-channel MOS process that uses currents made up of positive charges. NMOS is a silicon-gate N-channel MOS process that uses currents made up of negative charges and is at least twice as fast as PMOS. CMOS, Complementary MOS, is nearly immune to noise, runs off almost any power supply, and is an extremely low-power circuit Technique.

MP - Multiprocessor. A system with more than one processor typically sued to refer to systems with more than one central processor.

MPP - Massively Parallel Processor. A machine that contains many processors, each with its own memory and optional I/O ports. This is know as independent processor architecture. Each processor runs its own operating system's code and is linked to all other processors through some form of interconnection fabric. This independent processor architecture is much more difficult to program than an SMP system, but it is easier to scale to large sizes. MPPs with more than 1,000 processors have been built.

MTBF - Mean Time Between Failures. Reliability rating indicating the expected failure rate of a product (hard drive) in power on hours (POH). Since manufacturers differ in the ways they determine the MTFB, comparisons of products should always take into account the MTBF calculation method.

MTTR - Mean Time To Repair. The average time it takes to repair a drive that has failed for some reason. This only takes into consideration the changing of the major subassemblies such as the circuit board or sealed housing. Component level repair is not included in this number as this type of repair cannot be performed in the field.

MTF - Modulation Transfer Function. The ration of contrast to maximum usable brightness. The MTF should be greater than 35%.

MX - The Intel Triton II motherboard chip. The MX supports DIMMs.

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Compiled by Scott McArdle, MagnaCom Limited. I hope this list has helped you and if there is an item that should be on this list, please let me know. Thanks. PS, I've spent 100's of hours maintaining this list, please don't be a LAMER.