Glossary of Computer Terms

Computer Terms Glossary

This page is meant to serve as a guide to the vast quantity of computer terms and acronyms in common use for the casual computer user. It is divided into two main sections, the first is dedicated to the basics and is meant more for beginners, while the second is meant instead to be used as a reference. In reality many of the terms in the second section are still quite common; the first section was deliberately kept as short as possible.

Terms in the second section may be looked up by either using the "find in page" function of your browser, or by appending "#term" (without the quotes and where term is the term of interest) to the "URL" or "go to" section of your browser, keeping in mind that case matters. The best method of searching for a term though is to use the Search Interface that will return not only the specific term sought but also other entries that reference it. Be aware that the terms referenced in the second part of this page will freely assume familiarity with the first part.

If you are instead actually trying to figure out what a particular filename extension means, you might instead try the filename extensions page.

If you want something added or see a problem with something already here (but keep in mind this guide is not meant to be overly technical) please send .


Computer memory is used to temporarily store data. In reality, computer memory is only capable of remembering sequences of zeros and ones, but by utilizing the binary number system it is possible to produce arbitrary rational numbers and through clever formatting all manner of representations of pictures, sounds, and animations. The most common types of memory are RAM, ROM, and flash.
MHz & megahertz
One megahertz is equivalent to 1000 kilohertz, or 1,000,000 hertz. The clock speed of the main processor of many computers is measured in MHz, and is sometimes (quite misleadingly) used to represent the overall speed of a computer. In fact, a computer's speed is based upon many factors, and since MHz only reveals how many clock cycles the main processor has per second (saying nothing about how much is actually accomplished per cycle), it can really only accurately be used to gauge two computers with the same generation and family of processor plus similar configurations of memory, co-processors, and other peripheral hardware.
A modem allows two computers to communicate over ordinary phone lines. It derives its name from modulate / demodulate, the process by which it converts digital computer data back and forth for use with an analog phone line.
The screen for viewing computer information is called a monitor.
In computer parlance a mouse can be both the physical object moved around to control a pointer on the screen, and the pointer itself. Unlike the animal, the proper plural of computer mouse is "mouses".
This originally indicated a capability to work with and integrate various types of things including audio, still graphics, and especially video. Now it is more of a marketing term and has little real meaning. Historically the Amiga was the first multimedia machine. Today in addition to AmigaOS, IRIX and Solaris are popular choices for high-end multimedia work.


Mac OS
Mac OS is the OS used on Macintosh computers. There are two distinctively different versions of it; everything prior to version 10 (sometimes called Mac OS Classic) and everything version 10 or later (called Mac OS X).
Mac OS Classic
The OS created by Apple and originally used by Macs is frequently (albeit slightly incorrectly) referred to as Mac OS Classic (officially Mac OS Classic is this original OS running under the modern Mac OS X in emulation. Mac OS combines the functionality of both an OS and a window manager and is often considered to be the easiest OS to use. It is partially multitasking but will still sometimes crash when dealing with a buggy program. It is probably the second most popular OS, next only to Windows 'XP (although it is quickly losing ground to Mac OS X) and has excellent driver support and boasts a fair selection of games. Mac OS will run on PowerPC and 68xx based machines.
Mac OS X
Mac OS X (originally called Rhapsody) is the industrial strength OS produced by Apple to run on both PowerPC and x86 systems (replacing what is often referred to as Mac OS Classic. Mac OS X is at its heart a variant of UNIX and possesses its underlying power (and the ability to run many of the traditional UNIX tools, including the GNU tools). It also was designed to mimic other OSes on demand via what it originally refered to as "boxes" (actually high-performance emulators); it has the built-in capability to run programs written for older Mac OS (via its "BlueBox", officially called Mac OS Classic) and work was started on making it also run Windows '95 / '98 / ME software (via what was called its "YellowBox"). There are also a few rumors going around that future versions may even be able to run Newton software (via the "GreenBox"). It provides a selection of two window managers built-in: Aqua and X-Windows (with Aqua being the default).
machine language
Machine language consists of the raw numbers that can be directly understood by a particular processor. Each processor's machine language will be different from other processors' machine language. Although called "machine language", it is not usually what people think of when talking about computer languages. Machine language dressed up with mnemonics to make it a bit more human-readable is called assembly language.
A Macintosh (or a Mac for short) is a computer system that has Mac OS for its OS. There are a few different companies that have produced Macs, but by far the largest is Apple. The oldest Macs are based on the 68xx processor; somewhat more recent Macs on the PowerPC processor, and current Macs on the x86 processor. The Macintosh was really the first general purpose computer to employ a GUI.
An x86 based system running some flavor of Mac OS.
A mainframe is any computer larger than a small piece of furniture. A modern mainframe is more powerful than a modern workstation, but more expensive and more difficult to maintain.
The Math Mark-up Language is a subset of XML used to represent mathematical formulae and equations. Typically it is found embedded within XHTML documents, although as of this writing not all popular browsers support it.
A million cycles per second, abbreviated MHz. This is often used misleadingly to indicate processor speed, because while one might expect that a higher number would indicate a faster processor, that logic only holds true within a given type of processors as different types of processors are capable of doing different amounts of work within a cycle. For a current example, either a 200 MHz PowerPC or a 270 MHz SPARC will outperform a 300 MHz Pentium.
The Merced is a RISC processor developed by Intel with help from Hewlett-Packard and possibly Sun. It is just starting to be released, but is intended to eventually replace both the x86 and PA-RISC processors. Curiously, HP is recommending that everyone hold off using the first release and instead wait for the second one. It is expected some day to be roughly as fast as an Alpha or PowerPC. It is expected to be supported by future versions of Solaris, Windows-NT, HP-UX, Mac OS X, and Linux. The current semi-available Merced processor is called the Itanium. Its overall schedule is way behind, and some analysts predict that it never will really be released in significant quanitities.
Loosely speaking, An old disk format sometimes used by CP/M, MS-DOS, and MS-Windows. No longer too common as it cannot deliver close to the performance of either SCSI or IDE.
Software designed to sit in between an OS and applications. Common examples are Java and Tcl/Tk.
The multi-purpose Internet mail extensions specification describes a means of sending non-ASCII data (such as images, sounds, foreign symbols, etc.) through e-mail. It commonly utilizes bcode.
Multimedia extensions were built into some x86 CPUs to provide better performance for certain operations, most notably graphics and sound. It is similar to AltiVec on the PowerPC CPUs. Like AltiVec, it requires special software for full performance benefits to be realized.
A movable object is a graphical object that is manipulated separately from the background. These are seen all the time in computer games. When implemented in hardware, MOBs are sometimes called sprites.
Modula-2 & Modula-3
Modula-2 is a procedural language based on Pascal by its original author in around the 1977 - 1979 time period. Modula-3 is an intended successor that adds support for object-oriented constructs (among other things). Modula-2 can be either compiled or interpreted, while Modula-3 tends to be just a compiled language.
A message of the day. Many computers (particularly more capable ones) are configured to display a MOTD when accessed remotely.
Motif is a popular commercial window manager that runs under X-Windows. Free work-alike versions are also available.
The DOS produced by Microsoft. Early versions of it bear striking similarities to the earlier CP/M, but it utilizes simpler commands. It provides only a CLI, but either OS/2, Windows 3.1, Windows '95, Windows '98, Windows ME, or GEOS may be run on top of it to provide a GUI. It only runs on x86 based machines.
MS-Windows is the name collectively given to several somewhat incompatible OSes all produced by Microsoft. They are: Windows CE, Windows NT, Windows 3.1, Windows '95, Windows '98, Windows ME, Windows 2000, and Windows XP.
A multi-user dimension (also sometimes called multi-user dungeon, but in either case abbreviated to "MUD") is sort of a combination between the online chatting abilities provided by something like IRC and a role-playing game. A MUD built with object oriented principles in mind is called a "Multi-user dimension object-oriented", or MOO. Yet another variant is called a "multi-user shell", or MUSH. Still other variants are called multi-user role-playing environments (MURPE) and multi-user environments (MUSE). There are probably more. In all cases the differences will be mostly academic to the regular user, as the same software is used to connect to all of them. Software to connect to MUDs can be found for most platforms, and there are even Java based ones that can run from within a browser.
Some OSes have built into them the ability to do several things at once. This is called multitasking, and has been in use since the late sixties / early seventies. Since this ability is built into the software, the overall system will be slower running two things at once than it will be running just one thing. A system may have more than one processor built into it though, and such a system will be capable of running multiple things at once with less of a performance hit.