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AVI - audio/video interleave

Next time you see a video clip on your Mac, there's a good chance that it's an AVI file. AVI is the file format used by Video. For Macintosh they are MPEG and QuickTime. In AVI, picture and sound elements are stored in alternate interleaved chunks in the file.


Any picture you see on the Web (or hot off a scanner, or on a page created with a desktop publishing application) is called a bitmap. As its name suggests, a bitmap is a map of dots--similar to what you see when you look at a newspaper photo under a strong magnifying glass--that looks like a picture when viewed from a distance. Bitmaps come in many file formats (GIF, JPEG, TIFF, BMP, PICT, and PCX, to name a few) and can be read by paint programs and image editors such as Adobe Photoshop.


Bluetooth is a short-range wireless technology that lets you connect computers, mobile phones, and handheld devices to each other and to the Internet. Bluetooth technology eliminates the need for the cables that connect devices together. Bluetooth-enabled devices connect wirelessly within a 10 meter (30 foot) range. Do not confuse bluetooth with Airport. Airport is wirelessly connectng to the internet and has a range of 150' (ten stories) from its base station.


If you can read this, it's highly likely that you're using a Web browser. In brief, a browser is your interface to the World Wide Web; it interprets hypertext links and lets you view sites and navigate from one Internet node to another. Among the companies that produce browsers are Mosaic, Netscape, and Microsoft, as well as commercial services like America Online.


Caches come in many types, but they all work the same way: they store information where you can get to it fast. A Web browser cache stores the pages, graphics, sounds, and URLs of online places you visit on your hard drive; that way, when you go back to the page, everything doesn't have to be loaded all over again. Since disk access is much faster than Internet access, this speeds things up.

CD-R - compact disc recordable

A CD-ROM format that enables you to record data onto compact discs so that regular CD-ROM drives can read it. With a CD-R drive, you can record data onto a recordable disc on different occasions, known to experts as multiple sessions.


A cookie is a small data file that certain Web sites write to your hard drive when you visit them. A cookie file can contain information such including a user ID that the site uses to track the pages you've visited. But the only personal information a cookie can contain is information you supply yourself. A cookie can't read data off your hard disk or read cookie files created by other sites.

CPU - central processing unit

The CPU--a highly complex silicon chip ranging from the size of a matchbook to wallet-sized --is your computer's brain, taking requests from applications and then processing, or executing, actions, aka operations. The faster your processor, the more operations it can execute per second. The more operations you have per second, the faster things happen in your applications; thus, games play more smoothly, and spreadsheets calculate more quickly. Sometimes the term CPU is also used to describe the whole box that contains the chip (along with the motherboard, expansion cards, disk drives, power supply, and so on). Both uses are widespread, but only the first is really accurate.

CRT - Cathode Ray Tube

An acronym for Cathode Ray Tub, CRT's are for all practical purposes, picture tubes. However, the term CRT has become the often used term for a computer station or monitor. With the coming of the new flat-panel computer, we are disguishing between as calling the older model the CRT iMac.


Science fiction writer William Gibson coined the term cyberspace in the perennial favorite novel Neuromancer. Gibson used the word to describe a virtual world of computer networks that his cyberpunk heroes "jacked into." Everyone else uses the word cyberspace loosely to refer to virtual reality, the Internet, the World Wide Web, and many other kinds of computer systems that users become immersed in. It's about as ill-defined a term as information superhighway, but it's much hipper.


When you use the same file over and over again, writing, rewriting, saving, and deleting parts of it on the same disk, the file becomes fragmented. That means that although you can't tell, your operating system is storing all the data from that file as separate packages of information, distributed on different parts of the disk. Although fragmentation does not lose the information contained in the file, it does eventually slow down access to the file itself, because the OS must search the whole disk to create the sum of the file's parts. Defragmentation collects all those parts into one stream of data again, speeding up your system.

DNS - domain name system

When you send email or point a browser to an Internet domain such as comcast.com, the domain name system translates the names into Internet addresses (a series of numbers looking something like this: The term refers to two things: the conventions for naming hosts and the way the names are handled across the Internet.

domain name

Looking for a domain name? You'll find it to the right of the @ sign in an email address, or about ten characters into a URL. Miss Mac's domain name is missmac.com. Domain names are issued by the National Science Foundation (NSF), and they come with different extensions based on whether the domain belongs to a commercial enterprise (.com), an educational establishment (.edu), a government body (.gov), the military (.mil), a network (.net), or a nonprofit organization (.org). See about Domain Names in my Troubleshooting section.

DSL - digital subscriber line

Digital subscriber lines carry data at high speeds over standard copper telephone wires. With DSL, data can be delivered at a rate of 1.5 mbps (around 30 times faster than through a 56-kbps modem).

DVD - digital versatile disc

Originally referred to as digital video discs, these high-capacity optical discs are now used to store everything from massive computer applications to full-length movies. While similar in physical size and appearance to a compact disc or a CD-ROM, DVD is a huge leap from its predecessor's 650MB of storage. A standard single-layer, single-sided DVD can store a whopping 4.7GB of data.


Ethernet is a standard for connecting computers into a local area network (LAN). The most common form of Ethernet is called 10BaseT, which denotes a peak transmission speed of 10 mbps using copper twisted-pair cable.

FireWire - Institute of Electrical and Electronics Engineers *

FireWire is Apple's cross-platform implementation of a high-speed serial data bus defined by IEEE* Standard 1394-1995 that is able to transfer large amounts of data between computers and peripheral devices. FireWire features simplified cabling and hot swapping, and provides a single plug-and-socket connection to which up to 63 devices can be attached with data transfer speeds up to 400 megabits per second. FireWire is designed to support much higher data rates than USB 1.0; both standards are expected to exist together, serving different device types. With the introduction of the new FireWire 800 standard, Apple now refers to the original standard as FireWire 400.
*This nonprofit U.S. engineering organization develops, defines, and reviews standards within the electronics and computer science industries.

FTP - file transfer protocol

This Internet protocol is used to copy files between computers--usually a client and an archive site. It's old-fashioned, it's a bit on the slow side, it doesn't support compression, and it uses cryptic Unix command parameters. But the good news is that you can download shareware or freeware apps that shield you from the complexities of Unix, and you can connect to FTP sites using a Web browser.

GIF - graphics interchange format

Most color images and backgrounds on the Web are GIF files. This compact file format is ideal for graphics that use only a few colors, and it was once the most popular format for online color photos. However, GIF has lost ground to the JPEG format when it comes to photos. GIF images are limited to 256 colors, but JPEGs can contain up to 16 million colors, and JPEGs can look almost as good as a photograph.

GUI - graphical user interface

A graphical user interface lets users interact with their computer via icons and a pointer instead of by typing in text at a command line. Popular GUIs, such as Sun Microsystem's OpenWindows, Microsoft's Windows, and Apple's Mac OS, have freed many users from the command-line interfaces like MS-DOS.

HTML - hypertext markup language

As its name suggests, HTML is a collection of formatting commands that create hypertext documents--Web pages, to be exact. When you point your Web browser to a URL, the browser interprets the HTML commands embedded in the page and uses them to format the page's text and graphic elements. HTML commands cover many types of text formatting (bold and italic text, lists, headline fonts in various sizes, and so on), and also have the ability to include graphics and other nontext elements.

HTTP - hypertext transfer protocol

The protocol used to transmit and receive all data over the World Wide Web. When you type a URL into your browser, you're actually sending an HTTP request to a Web server for a page of information (that's why URLs all begin with "http://"). HTTP1.1, the latest version, is currently undergoing revisions to make it work more efficiently with TCP/IP.


A small picture or image that represents an object, a folder, or a program. Clicking or double-clicking icons launches programs, opens windows, and executes commands.

ISP - Internet Service Provider

Once upon a time, you could only connect to the Internet if you belonged to a major university or had a note from the Pentagon. Not anymore: ISPs have arrived to act as your (ideally) user-friendly front end to all that the Internet offers. Most ISPs have a network of servers (mail, news, Web, and the like), routers, and modems attached to a permanent, high-speed Internet "backbone" connection. Subscribers can then dial into the local network to gain Internet access--without having to maintain servers, file for domain names, or learn Unix.

JPEG - Joint Photographic Experts Group

This file format for color-rich images was developed by the Joint Photographic Experts Group committee. JPEG compresses graphics of photographic color depth better than competing file formats like GIF, and it retains a high degree of color fidelity. This makes JPEG files smaller and therefore quicker to download. You can choose how much to compress a JPEG file, but since it is a lossy format, the smaller you compress the file, the more color information will be lost. JPEG files can be viewed by a variety of downloadable software on both the PC and Mac.


Graphics files are big, and most file formats (such as BMP, TIFF, PICT, and PCX) are inefficiently coded, so they are larger than they need to be. So how do graphics programmers save disk space? They develop compression techniques. Graphics compression techniques fall into two camps: lossless and lossy. Lossless techniques throw away redundant bits of information without affecting the quality of the image. Lossy techniques, such as JPEG, crunch files down smaller, but they throw out image quality in the process. Most of the time, however, you can't see the difference in image quality unless you try to print the graphics on a professional imagesetter.


Modern operating systems are typically built in layers, with each layer adding new capabilities, such as disk access techniques or a graphical user interface. But the essential layer, the foundation on which the rest of the operating system rests, is typically called a kernel. In general, the kernel provides low-level services, such as memory management, basic hardware interaction, and security. Without the kernel, your system would stop.

MP3 - MPEG-1, Layer 3

MP3 is a codec* that compresses standard audio tracks into much smaller sizes without significantly compromising sound quality.
*codec (coder/decoder or compression/decompression algorithm) As the name implies, codecs are used to compress and decompress various types of data, particularly those that would otherwise use up inordinate amounts of disk space, such as sound and video files.

OCR - optical character recognition

When your computer gets a fax or scans in text, all it sees are graphical bits on a virtual page. That text is not usable, searchable, or editable. If you pass the page through an OCR program, the software converts the shapes on it into a text document. However, few documents are perfectly recognized and the errors are frequent if the type is small or the scan unclear. But the conversion is more often faster than typing text manually.

OS - operating system

A computer by itself is essentially dumb bits of wire and silicon. An operating system knows how to talk to this hardware and can manage a computer's functions, such as allocating memory, scheduling tasks, accessing disk drives, and supplying a user interface. Without an operating system, software developers would have to write programs that directly accessed hardware--essentially reinventing the wheel with every new program. With an operating system, such as Mac OS 9 or Mac OS X, developers can write to a common set of programming interfaces called APIs (application programing interface) and let the operating system do the dirty work of talking to the hardware.

PDF - Portable Document Format

This Adobe technology is a popular way of formatting documents in such a way that they can be viewed and printed on multiple platforms using the freely available Adobe Acrobat Reader.


This term refers to a type of program that tightly integrates with a larger application to add a special capability to it. The larger app must be designed to accept plug-ins, and the software's maker usually publishes a design specification that enables people to write plug-ins for it. Some notable applications designed around a plug-in architecture are Adobe Photoshop, Internet Explorer and Netscape. Notable examples of plug-ins are Shockwave, RealPlayer and Flash for your internet browsers.

PPP - point-to-point protocol

PPP is the Internet standard for serial communications. Newer and better than its predecessor, SLIP, PPP defines how your modem connection exchanges data packets with other systems on the Internet.


Developed by Apple Computer, QuickTime is a method of storing sound, graphics, and movie files. If you see a MOV file on the Web or on a CD-ROM, you'll know it's a QuickTime file. Although QuickTime was originally developed for the Macintosh, player software is now available for Windows and other platforms. If you don't have a QuickTime player, you can always download versions for either Mac or PC from Apple's Web site.

RAM - random access memory

When you run an application like AppleWorks, the program is called up from its permanent storage area (like the hard drive, floppy disk, or CD-ROM) and moved into the RAM, where it sends requests to the CPU. Your computer should have as much RAM as you can afford so it can work efficiently. It also pays to have lots of memory in your system because some operating systems, including OS 9, swap applications from memory to your hard drive when the RAM gets filled. That means that instead of having your speedy RAM sending out requests, the OS sends the work to be done by the much slower hard drive.


This piece of hardware does what it says: it routes data from a local area network (LAN) to a phone line's long distance line. Routers also act as traffic cops, allowing only authorized machines to transmit data into the local network so that private information can remain secure. In addition to supporting these dial-in and leased connections, routers also handle errors, keep network usage statistics, and handle security issues.

RTF - rich text format

This file format, developed by Microsoft, enables you to save text files in your word processor with formatting, font information, text color, and some page layout information intact. Sure, saving an AppleWorks file in AppleWorks format does the same thing, but saving it in this rtf format is intended for exchange among all kinds of word processors, both PC and Mac.

SCSI - Small Computer System Interface

While the PC was settling for rankly inferior alternatives, the Mac adopted SCSI as its expansion standard. With SCSI, you could add up to seven new devices to your computer. It's a robust standard, but it requires some system overhead, slows down your computer's start-up, and demands that during installation you handle device ID administration and a process called termination that closes the SCSI circuit. Pronounced "scuzzy" by those in the know. Newer Macs use USB (universal serial bus) and firewire connections.


Shareware is the wonderful alternative to commercial software. Available from centralized archives on the Internet and local bulletin board systems (or sometimes via CD-ROM or floppy), shareware is copyrighted but works on the honor system. You have a specified time period to try out the software for free; if you continue to use it, you're expected to register the program and pay a fee to its developer. (Some programs are partially disabled, stop working after a set period of time, or contain "nag screens" that pop up frequently to encourage you to register.) Registration fees are usually no more than $50, and some selfless developers ask only that you send a postcard letting them know you like their product. Registering often gets you full documentation or free software updates--not to mention a clear conscience. Shareware that doesn't involve a fee is called freeware.


SIT files are created by Aladdin Systems' Stuffit compression and decompression software. If you see a file with the extension .sit, you'll need a decompression program to open it. And although such files are typically compressed using Macintosh software for other Mac users, you can also open them using some PC programs, too.

SMTP - simple mail transfer protocol

When you're exchanging email on the Internet, SMTP is what keeps the process orderly. It's a protocol that regulates what goes on between the mail servers.


Data is streaming when it's moving quickly from one chunk of hardware to another and doesn't have to be all in one place for the destination device to do something with it. When your hard disk's data is being written to a tape backup device, it's streaming. When you're watching a QuickTime movie on the Internet, it's not streaming, because the movie must be fully downloaded before you can play it.

TCP/IP - transmission control protocol/Internet protocol

These two protocols were developed by the U.S. military to allow computers to talk to each other over long distance networks. IP is responsible for moving packets of data between nodes. TCP is responsible for verifying delivery from client to server. TCP/IP forms the basis of the Internet, and is built into every common modern operating system (including all flavors of Unix, the Mac OS, and the latest versions of Windows).

TIFF - tagged image file format

This graphics file format was designed to be the universal translator of the graphics world back in the 1980s when sharing graphics across computing platforms was a great headache. TIFF can handle color depths ranging from one-bit (black and white) to 24-bit photographic images with equal ease. Like any standards, however, the TIFF developed a few inconsistencies along the way: some graphical software companies estimate that there are more than 50 variations on the TIFF format.

TWAIN - toolkit without an interesting name

While there are some who claim that TWAIN stands for toolkit without an interesting name, in fact it stands for nothing but itself. But what is it? TWAIN is an interface standard that should be on the checklist of anyone buying a scanner or OCR, graphics, or fax software. If your scanner supports TWAIN, you can use any TWAIN-compliant software to run it. TWAIN's signature command is Acquire--if you spot the Acquire option under a program's File menu, you know the software is TWAIN-compliant.


Described by one of its developers as "a weak pun on Multics" (which was an experimental, time-sharing operating system at Bell Labs in the 1960s), Unix took off in the early 1970s as a general-purpose operating system. Since much of the Internet is hosted on Unix machines, the OS took on a new surge of popularity in the early 1990s. Unix comes in many flavors--including Xenix, Ultrix, GNU, and Linux--and runs on a variety of platforms, which makes its development a subject of widespread discussion. But the truly great debate involves how to style the word itself: should it have an initial capital (Unix)? Or should it be in all caps (UNIX)? Since the operating system itself is case-sensitive, the debate rages. Bell Labs' implementation of Unix is trademarked in all caps; for the other implementations, it's optional. Mac OS X is our newest OS and is based on Unix.

URL - uniform resource locator or universal resource locator

URLs are the Internet equivalent of addresses. How do they work? Like other types of addresses, they move from the general to the specific (from zip code to recipient, so to speak). Take this URL, for example:
First you have the protocol:

then the server address or domain:

and finally the directory:
in which the file gloss.html resides.

Two debates rage: first, does the U stand for uniform or universal? Universal was the original definition of choice but was deemed by most to be too ambitious, and the more frequently used uniform was instated by the now-defunct URI Working Group. Second, is URL pronounced "you are ell," or does it rhyme with hurl? Both pronunciations are widely used.

USB - universal serial bus

Imagine replacing all those ports on the back of your Mac--mouse, keyboard, serial, parallel, joystick, and more with a single port. Now imagine you can daisy-chain as many as 127 peripherals off that port and use them all at once. Finally, imagine that the port supports data transfer rates up to 12MB/sec, making it suitable for even high-bandwidth applications such as video. Imagine no more. USB, designed by a consortium of PC manufacturers including Compaq, Digital, and IBM, can do all this and more. USB-ready systems and peripherals hit the market en masse in 1997 and are now the industry standard. Apple implemented firewire which is able to transfer large amounts of data between computers and peripheral devices. Macs purchased today have both USB and firewire ports.

If you would like a really concise glossary, Apple has one here.

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