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 .


Chatting is like e-mail, only it is done instantaneously and can directly involve multiple people at once. While e-mail now relies on one more or less standard protocol, chatting still has a couple competing ones. Of particular note are IRC and Instant Messenger. One step beyond chatting is called MUDding.
To press a mouse button. When done twice in rapid succession, it is referred to as a double-click.
A point of attention on the computer screen, often marked with a flashing line or block. Text typed into the computer will usually appear at the cursor.


C is one of the most popular computer languages in the world, and quite possibly the most popular. It is a compiled langauge widely supported on many platforms. It tends to be more portable than FORTRAN but less portable than Java; it has been standardized by ANSI as "ANSI C" -- older versions are called either "K&R C" or "Kernighan and Ritchie C" (in honor of C's creators), or sometimes just "classic C". Fast and simple, it can be applied to all manner of general purpose tasks. C compilers are made by several companies, but the free GNU version (gcc) is still considered one of the best. Newer C-like object-oriented languages include both Java and C++.
C# is a compiled object-oriented language based heavily on C++ with some Java features.
C++ is a compiled object-oriented language. Based heavily on C, C++ is nearly as fast and can often be thought of as being just C with added features. It is currently probably the second most popular object-oriented language, but it has the drawback of being fairly complex -- the much simpler but somewhat slower Java is probably the most popular object-oriented language. Note that C++ was developed independently of the somewhat similar Objective-C; it is however related to Objective-C++.
The Commodore 64 computer to this day holds the record for being the most successful model of computer ever made with even the lowest estimates being in the tens of millions. Its big brother, the Commodore 128, was not quite as popular but still sold several million units. Both units sported ROM-based BASIC and used it as a default "OS". The C128 also came with CP/M (it was a not-often-exercized option on the C64). In their later days they were also packaged with GEOS. Both are based on 65xx family processors. They are still in use today and boast a friendly and surprisingly active user community. There is even a current effort to port Linux to the C64 and C128 machines.
The common desktop environment is a popular commercial window manager (and much more -- as its name touts, it is more of a desktop environment) that runs under X-Windows. Free work-alike versions are also available.
Some computer devices support chaining, the ability to string multiple devices in a sequence plugged into just one computer port. Often, but not always, such a chain will require some sort of terminator to mark the end. For an example, a SCSI scanner may be plugged into a SCSI CD-ROM drive that is plugged into a SCSI hard drive that is in turn plugged into the main computer. For all these components to work properly, the scanner would also have to have a proper terminator in use. Device chaining has been around a long time, and it is interesting to note that C64/128 serial devices supported it from the very beginning. Today the most common low-cost chainable devices in use support USB while the fastest low-cost chainable devices in use support FireWire.
character set
Since in reality all a computer can store are series of zeros and ones, representing common things like text takes a little work. The solution is to view the series of zeros and ones instead as a sequence of bytes, and map each one to a particular letter, number, or symbol. The full mapping is called a character set. The most popular character set is commonly referred to as ASCII. The second most popular character set these days is Unicode (and it will probably eventually surpass ASCII). Other fairly common character sets include EBCDIC and PETSCII. They are generally quite different from one another; programs exist to convert between them on most platforms, though. Usually EBCDIC is only found on really old machines.
Complex instruction set computing is one of the two main types of processor design in use today. It is slowly losing popularity to RISC designs; currently all the fastest processors in the world are RISC. The most popular current CISC processor is the x86, but there are also still some 68xx, 65xx, and Z80s in use.
A command-line interface is a text-based means of communicating with a program, especially an OS. This is the sort of interface used by MS-DOS, or a UNIX shell window.
The Common Business Oriented Language is a language developed back in 1959 and still used by some businesses. While it is relatively portable, it is still disliked by many professional programmers simply because COBOL programs tend to be physically longer than equivalent programs written in almost any other language in common use.
If a program is compiled, its original human-readable source has been converted into a form more easily used by a computer prior to it being run. Such programs will generally run more quickly than interpreted programs, because time was pre-spent in the compilation phase. A program that compiles other programs is called a compiler.
It is often possible to remove redundant information or capitalize on patterns in data to make a file smaller. Usually when a file has been compressed, it cannot be used until it is uncompressed. Image files are common exceptions, though, as many popular image file formats have compression built-in.
A cookie is a small file that a web page on another machine writes to your personal machine's disk to store various bits of information. Many people strongly detest cookies and the whole idea of them, and most browsers allow the reception of cookies to be disabled or at least selectively disabled, but it should be noted that both Netscape and MSIE have silent cookie reception enabled by default. Sites that maintain shopping carts or remember a reader's last position have legitimate uses for cookies. Sites without such functionality that still spew cookies with distant (or worse, non-existent) expiration dates should perhaps be treated with a little caution.
An early DOS for desktops, CP/M runs on both Z80 and the x86 based machines. CP/M provides only a CLI and there really is not any standard way to get a window manager to run on top of it. It is fairly complex and tricky to use. In spite of all this, CP/M was once the most popular DOS and is still in use today.
If a bug in a program is severe enough, it can cause that program to crash, or to become inoperable without being restarted. On machines that are not multitasking, the entire machine will crash and have to be rebooted. On machines that are only partially multitasking the entire machine will sometimes crash and have to be rebooted. On machines that are fully multitasking, the machine should never crash and require a reboot.
A Cray is a high-end computer used for research and frequently heavy-duty graphics applications. Modern Crays typically have Solaris for their OS and sport sixty-four RISC processors; older ones had various other configurations. Current top-of-the-line Crays can have over 2000 processors.
Crippleware is a variant of shareware that will either self-destruct after its trial period or has built-in limitations to its functionality that get removed after its purchase.
Cascading style sheets are used in conjunction with HTML and XHTML to define the layout of web pages. While CSS is how current web pages declare how they should be displayed, it tends not to be supported well (if at all) by ancient browsers. XSL performs this same function more generally.