Mac
(1) Short for Macintosh. See also Apple.

(2) See MAC sub-layer.
MAC address
See MAC sub-layer.
MacBinary
See bin.
machine language
See low-level language.
Mac OS
Macintosh Operating System. The Mac OS is the operating system for by Apple Computer. The Macintosh OS came out in 1984. System 1 (1984) through System 7 (1999). Mac OS 8 (1997) through Mac OS 9.2.2 (2002, the last of "Classic" Mac). Mac OS X (2001) introduced the Mac OS rebuilt on a UNIX. See also these off-site links: Mac OS [W]. "A History of Apple's Operating Systems".
MAC sub-layer
Media Access Control sub-layer. A sub-layer of the OSI Data Link Layer. It deals with the concept of who speaks when on a network. EG: IEEE 802.3 deals with Ethernet's MAC sub-layer.

The MAC sub-layer handles MAC addresses. A MAC address is a 12 digit hexadecimal code stored in the ROM chip of a NIC (Network Interface Card). A computer is uniquely identified on a network by its MAC address. There are 16^12 or approximately 2.8E14 possible values for a 12 digit hexadecimal number. 
mainframe architecture
Single-tier model. The original kind of computer network in which there was a main computer all the user interface, applications, and data while the users had dummy terminals. An example would be the old IBM computers you see in old movies with the big rolls of tape spinning around. IBM introduced the System/360 in the 1960s. More modern models include the S/390. See also client-server architecture and NCA.
main memory
See processing memory.
man
A UNIX command which gets information on other commands, thus some people will refer you to the "man pages."
MAN
Metropolitan Area Networks. Computers and LANs linked over a metropolitan area. A city sized WAN. This is usually accomplished with media such as fiber optics and possibly utilizing the metropolitan phone, cable, and/or subway companies.
Management Information Base
See MIB.
Mandelbrot
See fractal.
mantissa
One of the older definitions of "mantissa" wasn't even mathematical: a "mantissa" was a minor addition or supplement, usu. an added statement. Later on, especially in the days of slide rules, the word "mantissa" referred to the fractional part of a common logarithm. EG:
log10 120 =
log10 (1.2 × 102) =
log10 (102 × 1.2) =
2 + log10 1.2 ~
2 + 0.079181

The 2 was the characteristic and the 0.079181 was the "mantissa".
markup language
A language that uses tags within a document to signify changes in presentation style or content. SGML, HTML, troff, and LaTeX are all examples of markup languages.
MCP
Microsoft Certified Professional. The original certification by Microsoft for installing and supporting their products. There are currently four certifications: MCPS (Microsoft Certified Product Specialist), MCSE (Microsoft Certified Systems Engineer), MCSD (Microsoft Certified Solutions Developer), and MCT (Microsoft Certified Trainer).
MDA
Monochrome Display Adapter. Video display of text only for a maximum of 80 characters x 25 lines.
mdb
.mdb. A database created with the Microsoft Jet Database Engine.
MDE
.mde. A Microsoft Access application with all the VBA removed so as to protect source code and to prevent changes to forms, reports, and modules.
MDI
Multiple Document Interface. The GUI of having documents of an the application appear as windows within the application. The application itself appears as a window within the OS. All of these windows have the usual abilities of regular windows, i.e. there can be several windows, the windows can be resized, minimized, or maximized, the windows can be opened or closed, etc.
MDRAM
Multibank Dynamic Random Access Memory. A memory circuit board developed by MoSys, Inc. MDRAM circuits have small banks of DRAM, each of which has its own I/O port that feeds to the common internal bus. This means that MDRAM is faster than DRAM since multiple banks can be written simultaneously. Additionally, an MDRAM circuit board can be made in smaller increments than regular DRAM. This is good for certain applications such as a video adapter which may only need 2.5 MB instead 4 MB.
me
.me. Extension on a file telling you to do something. EGs: READ.ME, TYPE.ME.
media

(0) Plural for an intervening substance through which something else is transmitted or carried on.

(1) The various files that provide text, images, audio, video, and applications.

(2) Whatever medium is used to communicate data. Media is usually the copper or fiber optic glass cables but data can also be sent through the air via electromagnetic frequencies such as infrared, microwave, or radio waves. Media is important because it is often half the cost of the network! See also my article on Media in Networks.

Media Access Control sub layer
See MAC sub layer.
megahertz
See MHz.
member
In OOP (object oriented programming), these are the elements that describe an object as an instance of a class. These are the properties, methods, and events that distinguish an object of a class from other objects of the same class.
member server
See domain controller.
meme
Pronounced meem. A contagious idea that replicates like a virus, passed on from mind to mind. Oxford professor Richard Dawkins coined the term meme to be analogous to gene. Memes function the same way genes and viruses do, by propagating through communication networks and face-to-face contact between people. EGs: melodies, icons, fashion statements and phrases.

Memetics is a field of study which postulates that the meme is the basic unit of cultural evolution. The idea is that cultural evolution is more important than biological evolution for sentient creatures in the short term. A meme complex denotes a group of mutually supporting memes that forms an organized belief system, such as a religion or cult.
memex
MEMory EXtender. A theoretical analog "computer" described by Vannevar Bush ("As We May Think". The Atlantic Monthly 1945.). The device was electronically linked to a library of resources such as books and films, where each could link to other resources. Sounds like the WWW, eh?
memory
The storage needed by a computer for its variables and constants. Here are the major divisions of memory:
  • storage memory v. processing memory.
  • RAM (Randomly Accessed Memory) v. SAM (Sequentially Accessed Memory).
  • stack memory v. heap memory.
MEMS
MicroElectroMechanical Systems. Aka smart matter. Machines the size of a mote of dust or smaller. Such devices exist and are a stepping stone to nanotechnology. EG: Toyota has already developed a microengine 0.7 mm in size.
menu
A group of commands and options that pop up when the group title is selected on the menu bar.
menu bar
A bar in window where the group titles of menus are listed. The menu bar is usually located underneath the title bar and above the toolbar, if there is one.
message board
Aka forum, newsgroup, discussion group. An online message board. People can post email-like messages to message boards and respond to messages on these message boards. A chain of messages is a thread. Message boards are either free, like Usenet, or at a cost, like some BBSes. Most message boards are public but some are restricted to particular groups. Usually a news reader application is needed as well as access to a news server. It is possible to access the non-binary content of Usenet via a browser with Groups.Google.com.
Message Oriented Middleware
See MOM.
meta data
Data about data. Meta data provides summary and parameter information about a set of data. This is key information like who, where, when, and how the data was transmitted, acquired, etc. HTML pages often have meta data in the heading.

Here's how I explained it to someone just a minute ago [2007-10-31t14:03:41Z]:
Metadata is data about data. For example a patient has data describing him, and some of that data is further described with other data (metadata). I think people get thrown off because "metahphysics" sounds so perplexing (as in "beyond physics") when "meta" just means "after" in Greek. "Metaphysics" was simply meant to describe the Aristotle's book that came after his book on "physics". In a similar fashion: "Metadata" is just additional data about the first piece of data.
Metclaf's Law
A rule of thumb that states that the value of a network is the square of the number of its nodes. It means that the whole is greater than the sum of its parts in a geometric fashion. It also means that a network with more nodes will get more traffic very quickly in a non-linear fashion, thus network growth has to be managed tightly. It is conceptually useful but practically useless, esp. for very large number of nodes, eg the Internet.
method
In OOP (Object Oriented Programming) the method of an object is an appendage to an object which thus provides the name of a function. Functions perform particular services or actions. EG: thing.sum (12,3.5,7). This is in contrast to a "property" which provides the name of a literal.
MFC
Microsoft Foundation Class. A class library by Microsoft used to speed the building of Windows applications. See also OWL.
MHT
.mht. MIME HTML, MHTML. See MHTML. A standard for including resources (such as images and sound files) in the same file as the HTML code by encoding the resources using the MIME type multipart/related.
MHTML
See MHT.
MHz
MegaHertz. One million cycles per second. The unit used in measuring the operational speed of a device such as a microprocessor or bus. Additionally, the data width, in bits at a time, of the I/O bus is also a good measuring stick. See also MIPS and FLOPS.
MIB
(1) Management Information Base. A format for data regarding the status of data flow of a particular device on a network. See also SNMP.
 
(2) Men In Black. Alleged agents of either secret government agencies or of extraterrestrials.
microelectromechanical systems
See MEMS.
microprocessor
See processor.
Microsoft
Microsoft Corporation. That lovable company that makes DOS, Windows 3.x, Windows 9X, Windows NT, Office, BackOffice, Visual Studio, etc. It was founded by Bill Gates and Paul Allen in 1975. MS is headquartered in Redmond, WA.  See also my section on Microsoft.
Microsoft CD-ROM Extension
See MSCDEX.
Microsoft Certified Professional
See MCP.
Microsoft Foundation Class.
See MFC.
Microsoft Management Console
See MMC.
middleware
(1) Software that facilitates communication between two heterogeneous systems. This can be network operating systems and protocol, or software that can distinguish and interface with different SQL servers. EG:
  • EDA/SQL (Enterprise Data Access/SQL) by Information Builders Inc. is a common SQL middleware that can recognize different formats, including DB2, Oracle, VSAM, and MS SQL Server.
  • SNA Server (System Networking Architecture) by Microsoft allows PCs to access mainframe databases directly, including DB2 and VSAM files.
  • Screen scraping is a technique that allows interfacing with mainframes by getting or putting text at precise positions on pre-existing "green screens" of mainframe applications.
(2) It may also be said that middleware refers to the dominant middleware platforms: Microsoft's COM+, OMG's CORBA, and Sun's EJB. Those platforms support component-oriented middleware and development of distributed applications.
MIDI
.mid or .midi. Musical Instrument Digital Interface. A standard format for recording music  that tends to have a "tin-ish electronic" sound quality. See also my article on Sound.
midrange computer
See minicomputer.
millipede
A MEMS technology that reads, writes data via a 2D array of miniature hole punches. As of 2005 IBM built a millipede that used 64x64 (4,096) cantilevers over a polymer film 10 mm x 10 mm.
MIME

Multipurpose Internet Mail Extensions. RFC1521. Originally an extension of SMTP (Internet e-mail) proposed in 1991 by Nathan Borenstein of Bellcore. MIME allows non-US-ASCII textual messages, non-textual messages, multipart message bodies, and non-US-ASCII information in message headers. In other words, MIME enables multi-media and multipart encoding. MIME's utility has been to extended to more apps than just e-mail. EG: Browsers also use MIME to identify the content of documents.

A newer version of MIME is S/MIME (Secure MIME) that supports encryption via RSA's public key encryption method.

MIME HTML
See MHT.
minicomputer
Aka midrange computer. A computer somewhere between a desktop PC and a mainframe. A common minicomputer is the IBS AS/400 with its built in DBMS called DB2/400.
MIPS
Million Instructions Per Second. An older method of measuring a computer's power and speed. It has fallen into disuse because of lack of standardization and because there are so many other factors that affect a computer's power and speed. See also FLOPS and MHz.
mirroring
See replication.
MIS
Management Information Systems.
miter joint
A corner that comes to a point. See also beveled joint.
MLM
Multi-Level Marketing. Pyramid scheme, eg Amway sells via MLM.
MMC
Microsoft Management Console. An interface similar to Windows Explorer that Microsoft uses to manage most of various Microsoft Back Office components including SQL Server and IIS. The different BO components are implemented in MMC as snap-ins, sort of like different faceplates.
MMX
Technology from Intel that speeds multimedia functions on PCs by adding 57 new instructions to the x86 set of instructions. These functions are supposed to provided richer color, smoother video, faster graphics, and incredible sound. Older Pentium and Pentium Pro systems do not have MMX enabled chips. Pentium II, P55C, AMD-K6, Cyrix 6x86MX and IDT WinChip C6 are all MMX enabled.
mod
See modulus.
Model-View-Controller
See MVC.
modem
(1) MODulator/DEModulator. Converts the binary on-and-off digital pulses of computers, received via a typical RS-232C circuit, into equivalent audio tones that can be transmitted over a typical analog telephone circuit, RJ-11, and vice versa.

Common rates of transfer are 1.2 kb/s, 2.4 kb/s, 9.6 kb/s, 14.4 kb/s, 28.8 kb/s, 33.6 kb/s, and 56.6 kb/s. Note the 56.6 kb/s modems come in three flavors (US Robotics x2, Rockwell K56 flex, and Lucent K56 flex) that are theoretically being combined under ITU V.90 standards.

External modems have codes or LED lights that indicate the interaction status between the modem and the UART microchip (Universal Asynchronous Receiver-Transmitter) in a computer. Here are the codes:
Code Meaning
AA Auto Answer. Ready for incoming calls. Unfortunately, this light may be off even if it is ready to receive.
CD Carrier Detect. The modem and the computer are talking, i.e. they have a carrier connection established.
HS High Speed. The modem happed to be ready to transfer at its maximum speed.
MR Modem Ready. Contrast this with TR.
OH Off Hook. The phone "picked up" and ready to use.
RD Receiving Data.
SD Sending Data.
TR Terminal Ready. The communication application on the computer is ready. Contrast this with MR.

(2) A device that provides connectivity through different media but does not actually modulate and demodulate. Currently that includes ISDN modems (64 or 128 kb/s), satellite modems (400 kb/s), DSL modems (9 Mb/s), and cable modems (30 Mb/s max; realistically download at 1.5 Mb/s and upload at 0.3 Mb/s or analog modem rates).
modulo
See modulus.
modulus
An arithmetic operator, sometimes represented by % or by mod, that yields the remainder after one number is divided into another. EG:  9%4 is 1. This is in contrast to integer division which divides two numbers but discards the modulus. EG: 9\4 is 2.
MOM
Message Oriented Middleware. A connection between applications based on the exchange of messages.

Message queuing MOMs have applications send messages to a queue that is checked by other application. This is like e-mail. A message queuing MOM can be made synchronous by waiting for a response.

Publish and subscribe MOMs have multiple messages out to multiple recipients. Furthermore recipients can subscribe to the MOM to ensure that the messages are more timely. This is like a website that informs you when it updates.
monitor
A hardware device, very much like a TV set, used for interfacing with a computer. Computer monitors use RGB standards whereas most TVs use NTSC (or PAL in Europe), but the two will effectively mergewhen High Definition TV (HDTV) becomes the norm.

See also my article on Video.
Monochrome Display Adapter
See MDA.
MOO
MUD object oriented; multi-user object oriented. MOO is like a chat room where the users are also developers who work collaboratively on code in real time.
Moore's Law
Initially this was an observation made in 1965 by Gordon Moore, co-founder of Intel, that the number of transistors per square inch on integrated circuits had doubled every year since the integrated circuit was invented. Moore predicted that this trend would continue through 1975 but it has continued beyond that. In subsequent years, the pace slowed down a bit, but data density has doubled approximately every 18 months, and this is the current definition of Moore's Law, which Moore himself has blessed.
 
Most experts, including Moore himself, expect Moore's Law to hold until 2020. By then the technology will be pushing the "Point One Limit." This is when creating chips with a laser beam smaller than 0.1 micron (roughly the width of a coil of DNA) will present problems as quantum theory problems come into play.
Morse code
The grandfather of ASCII.
A.-        B-...      C-.-.      D-..
E.         F..-.      G--.       H....
I..        J.--       K-.-       L.-..
M--        N-.        O---       P.--.
Q--.-      R.-.       S...       T-
U..-       V...-      W.--       X-..-
Y-.--      Z--..      (.).-.-.-  ,--..--
?..--..    1.----     2..---     3...--
4....-     5.....     6-....     7--...
8---..     9----.     0-----
motherboard
The main circuit board on a computer and everything else in the system eventually connects to it. Unlike a daughter board, it is not removable. The actual CPU chip is in a socket on the motherboard. The socket usually comes in a 168/169 pin variety or the 237/238 pin variety, i.e. the CPU chip socket will have either 3 or 4 rows of pinholes surrounding it.
Mosaic
The first web browser. It was developed in 1993 by the NCSA team led by Marc Andreesen. He later went on to develop Netscape.
mov
.mov. See QuickTime.
mozilla
MOsaic godZILLA. Mosaic killer. A pseudonym for Netscape's browser since Mosaic was the biggest browser before Netscape Navigator.
MP3
.mp3. Moving Pictures Experts Group audio layer 3. A subset of MPEG that can compress 20 MB into 1.4 MB, i.e. the equivalent of taking two minutes of CD music and putting it onto a floppy disk. There are three coding schemes in MPEG to compress audio (layer 1, layer 2, and layer 3). Layer 3 supposedly compresses by removing redundant and irrelevant parts of the signal. MP3 compresses CD quality (1411.2 kb/s) to FM radio rates (112-128 kb/s, roughly a factor of 12). This is small enough for the Internet. MP3s can be played back using a ripper like Microsoft Media Player or RealNetwork's RealPlayer. See also my article on Sound.
MPC
Multimedia Personal Computer. Specifications set by the SPA for guidelines that describes the quality of multimedia. MPC1 came out in 1991 and MPC2 came out in 1993. MPC3 came out in 1996 and expects 8 Mb RAM, 540 Mb hard drive space, VGA, full motion video, 4X CD, 250 ms avg. seek time, 16 bit sound board, MIDI, 3 W per channel speakers, and at least Windows 3.11 or DOS 6.0.
MPEG
Moving Pictures Expert Group. See MPG.
MPG
.mpg or .mpeg. Moving Pictures Expert Group. (Often pronounced "em-peg".)

(1) A group in ISO.

(2) A family of formats and standards developed by the ISO group for digital video compression. Video file format. Currently the standard with competition such as Video for Windows, Indeo, and Apple's QuickTime.

MPEG compresses by storing changes from frame to frame instead of each entire frame. The data is then encoded via DCT. This involve lossy compression but the missing data is usually imperceptible by the human eye.

MPEG-1 provides 30 frames/s (fps) with frame resolutions of 352x240 pixels. This is slightly below VHS quality.

MPEG-2 provides 60 fps with frame resolutions of 720x480 and 1280x720, in addition to CD quality audio. This is sufficient for most TV standards, including NTSC, PAL, and even HDTV. In MPEG-2 format, 2 hours of video is only a few gigabytes. DVD utilizes MPEG-2. Although there is a lot of processing power required to encode video into MPEG-2 format, it does not take much to decompress an MPEG-2 data stream.

MPEG-3 was skipped by ISO. See MP3.

MPEG-4 is being worked on by ISO. It will be based on Apple's QuickTime.
MRAM
Magnetoresistive RAM. MRAM uses magnetic states instead of electrical charges to store data. This is essentially the same physics of analog audio tapes, video tapes, and hard drives. The key difference between RAM and regular (electrical) RAM is that MRAM retains its data when the power is off whereas regular RAM forgets everything without power. This should enable computers to start up much more quickly. MRAM also has the potential to by 6x or more faster than SRAM, as well as being very dense and thus small.
MS
See MicroSoft.
MSCDEX
MicroSoft CD-ROM EXtension. A 16 bit driver for DOS and Windows 3.X which enables the system to recognize and control CD-ROM players. The file is usually called MSCDEX.EXE. See also CDFS.
MSP
Managed Service Providers. All the external help that a company can enlist to run itself. For computers, this includes companies that can provide remote connections, network management, user support, security, and application hosting. MSPs include ISPs, local and distant telcos, and VANs (Value Added Networks).
MUD
Multi-User Dungeon or Domain.
MUD object oriented
See MOO.
Multics
Multiplexed Information and Computing Service. A mainframe timesharing operating system that was developed by Fernando J. Corbató and his team at MIT. Multics came into general use at MIT by 1969,  and in 1973 it was commercially offered by Honeywell until 2000. Unix is a play on Multics where "UNplexed" was substituted for "Multiplexed" to make "Unics".
multimedia
A presentation that has a mix of media above and beyond just text and pictures. Multimedia usually refers to the addition of audio, video, or both. Streamed media is displayed to the user as they download it. Webcast streamed video is live, ie not prerecorded. Non-streamed multimedia may be downloaded and then viewed at the user's leisure.
Multiple Document Interface
See MDI.
multiplex
To combine two or more signals (whether analog or digital) for transmission over a single line or media. An obvious example would be the simultaneous broadcast of different radio stations on different frequencies over the airwaves. A computer usage would be to combine channels for transmission over a high speed data link such as a T1 or frame relay line. To demultiplex would be to separate the multiple signals.
 
Here are the most common methods of multiplexing: FDM (Frequency Division Multiplexing), WDM (Wavelength Division Multiplexing), TDM (Time Division Multiplexing), and STDM (Statistical Time Division Multiplexing, i.e. weighted or dynamically assigned time slots).
multiport repeater
See hub.
multiprocessing
The utilization of more than one CPU in a single computer system. Asymmetric multiprocessing assigns each CPU to specific types of tasks. Symmetric multiprocessing has each CPU free to whatever tasks comes its way. Parallel processing has dozens of CPUs working together.
Multipurpose Internet Mail Extensions
See MIME.
multi-tapping
Multi-tapping is a system for entering characters into a system using a telephone keypad, EG: The letters A, B, and C are associated with the number 2, so to enter B, you would tap the number 2 twice. T9 (Text on 9 keys) is a system that uses software to predict what word you intend to enter on a telephone keypad. I find both systems annoying and prefer a full alphanumeric keypad.
multitasking
The ability of an OS to run multiple processes (tasks, programs) at a time. In true multitasking, ie multiprocessing, an OS simultaneously runs a different processes on different processors. For computers with a single processor, multitasking is simulated by time slicing the processor's computing cycles between different tasks.

Time slicing can be done preemptively. The OS gives each process a little slice of processing time, and then alternates between the processes.

Time slicing can also be done cooperatively. Each process hangs onto the processor until its its task is done.
multithreading
The ability of an OS to break a process into parts, called threads, which can be executed at the same time.
  • Single-Threaded. All instances of a component share the same "apartment" and the same thread. Functions (methods) execute one at a time. This is not multithreading at all.
  • Apartment-Threaded. Each instance of a component has its own apartment and its own single thread. Methods in separate apartments can execute simultaneously.
  • Free-Threaded. All instances of a component share the same apartment but have multiple threads. Methods within that apartment can execute simultaneously. There are two points regarding free threading:
    • Trans-apartment calls require proxies and thus have additional overhead.
    • The threads within an apartment don't require proxies but must be synchronized with each other.
  • Both-Threaded. Acts as apartment- or free-threaded depending on the calling object:
    • When the component is called from an apartment-threaded object, then the component makes another apartment with a single thread.
    • When the component is called from a free-threaded apartment, then the component acts as another thread in the calling apartment. These threads must be synchronized.

Microsoft multithreading requires an understanding of COM, C++, and Win32.
Multi-User Dungeon or Domain
See MUD.
munge
Originally a Scottish word for imperfectly transforming or munching up into a mess. The word munge has been used in computers since at least 1958. In acronym form it is explained as "Mash Until No Good", "Mung Until No Good", "Modify Until Not Easily Guessed". A mild munge may be a simple form of encryption (EG: Change "hello" into "h3llo".). A strong munge —especially a fairly random one— is fairly irreversible (EG: Change "hello" to "h3llo" to "#B110" to "#BH.").
Musical Instrument Digital Interface
See MIDI.
MuTeX
See TeX.
MVC
Model-View-Controller. A software architecture that tries to keep the Model (business logic; domain logic) separate and distinct from the user interface (UI) which in turn should be broken up into View (presentation; results) and Controller (application; form). In a typical Web app, the user interacts with an HTML form (Controller), where the user input is parsed with business logic (Model), and results are returned with an HTML presentation (View). MVC was first described in 1979 by Trygve Reenskaug, then working on Smalltalk at Xerox PARC.
MVS
The OS for IBM's mainframes.

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