FILE FORMATS AND EXTENSIONS

While surfing the World Wide Web, you will most likely encounter many different types of electronic files. The way you can identify the type is by looking at its extension, which is usually expressed as a dot followed by 2 to 4 letters. You need to identify file type to know whether it will work on your computer, and whether you will need a particular type of software to decompress, play, or view it.

Many sites make files available for both Windows and Mac operating systems. Your browser has the ability to identify and display some but not all of them, and new ones appear all the time. Most of the files will be either text, graphics, audio or video files. Some may be compressed, others not. The most common compressed files are those with extensions like .ZIP, .SIT and .TAR. These extensions represent popular compression formats for the PC, Macintosh, and UNIX. They may be single files or groups of files that have been bundled together into a single archive. An archive file can contain video or graphics files and often contains software programs with related documentation. Occasionally you may encounter files with multiple extensions like .tar.gz, which usually means more than one type of software was used to compile and compress the file.

The most common graphics file formats on the Web are those with the extensions .jpg and .gif. The .jpg is short for JPEG which is a popular compression standard for photographs and other images. The .gif extension stands for Graphics Interchange Format, a standard developed by CompuServe in the late 1980s. Both these graphics formats are platform-independent, which means you can use them on a PC, Mac or UNIX machine as long as you have a viewer for them.

For video, the popular extensions are .AVI for the PC, .MPG (short for MPEG) which is platform-independent, but requires its own player, and .MOV and .QT for QuickTime movies. QuickTime was initially developed just for the Macintosh, but are now run on Windows and UNIX, too.

The most popular sound files seem to be .MP3 for both Mac and PCs. Other file formats include .AIFF (for Mac); .AU for Mac and UNIX; .WAV for the PC; and .RA for Real Audio, a proprietary system for delivering and playing streaming audio on the Web. All of the file formats found on the Internet can be broken into one of two types:  ASCII format and BINARY format. ASCII files are text files you can view with a DOS Editor or any word processor. Binary files contain non-ASCII characters. If you display a binary file on your screen, you will see a lot of strange symbols and characters.

Plain Text (ASCII) Files

.html/.htm

The language in which Web documents are authored. File Type: ASCII This file type requires a web browser, such as Netscape Navigator or Internet Explorer, for viewing.

.txt

A plain (ASCII) text file. File Type: ASCII These files can be viewed with a word processor like Microsoft Word or a simple text editor like Simple Text or BBEdit for the Mac. For the PC you can use the Notepad that came with your Windows operating system or a shareware program called Programmer's File Editor (pfexxx.zip).

Formatted Documents

.doc

A common PC format for formatted text files. File Type: ASCII
Although you may occasionally come across files with this extension that are not text documents, usually they are documents that were created using Microsoft Word or WordPerfect for Windows. If you don't have one of these programs, try Wordview to view MS Word documents.

.pdf

Portable Document Format, a proprietary format developed by Adobe Systems, Inc. that allows formatted documents (including brochures or other documents containing artwork) to be transferred across the Net so they look the same on any machine. File Type: Binary
This file type requires an Adobe Acrobat Reader to view files. This is available for Mac, Windows and UNIX, directly from Adobe.

.ps

A PostScript file. File Type: ASCII Though it is technically a plain text file, it is essentially unreadable except by a Postscript printer or with the help of an on screen viewer like Ghostscript, which is available for Mac, Windows, and UNIX.

Compressed and Encoded Files

.arc

An old and inefficient format for archiving and compression. File Type: Binary
If you need to exchange files with an older operating system or have old files to read on a new machine, you may need an ARC program. Stuffit Expander for Windows will work for the PC (sitexxx.exe). For the Mac try something called ARCMac.

.arj

A somewhat common format for MS-DOS machines, especially in Europe. File Type: Binary
It is fairly slow and in some cases may do a better job than the more common gzip, zip and Stuffit formats. You can use Stuffit Expander for Windows or WinZIP. On the Mac, try UnArjMac.

.bin

A Mac binary II Encoded File. File Type: Binary
This file type requires Stuffit Expander for the Mac. You download this type of file as MacBinary or Binary.

.exe

A DOS or Windows program or a self-extracting file. File Type: Binary
If this is an executable (self-extracting) file, then it can usually be launched by double-clicking on the icon on your desktop. This is the only way to tell if it is an executable file.

.gz/gzip

The GNU Project's compression program, most commonly used for UNIX and PC files. File Type: Binary
For the Mac, use MacGZIP. There are several Windows-based GZIP uncompressors available.

.hqx

A common Macintosh encoding format. File Type: Binary
A file with the .hqx extension is a Macintosh binary file that has been converted into ASCII text so it can be safely transferred across the Net. You can use Stuffit Expander to decode on the Mac or BinHex4 (binhex4.bin) to create and extract Binhex 4 files. Use BinHex13 (binhex13.zip) on a Windows machine to un-binhex it.

.sit

A Macintosh file that has been compressed using a program called Stuffit. File Type: Binary
To unstuff a file with a .SIT extension, you need a program called Stuffit Deluxe or you can use Stuffit Expander for the Mac or for Windows. All three versions can decompress other file formats as well.

.sea

A Macintosh self-extracting archive file. File Type: Binary
An archive file is usually a collection of files that have been combined into one to make it easy to download. Because the archive is self-extracting, you don't need any special application or utility to launch it. You simply click on the icon from the Macintosh desktop and it decompresses and unbundles the files.

.tar/.tar.gz/.tar.Z/.tgz

A UNIX archiving scheme that is also available for PCs. File Type: Binary
Tar, which is short for Tape ARchive, can archive files but not compress them, so .tar files are often gzipped, which is why you might occasionally encounter the file extension .tar.gz. To download and use .tar files on a Mac, you use a program called Tar. For Windows you can use WinZIP to view and extract archive files.

.uu

A UUencoded file. File Type: Binary
UUencoding allows the user to convert binary data into text so it can be sent via e-mail. You don't often see the .uu extension because many e-mail programs automatically decode it in a way that is invisible to you. If your mail program doesn't UUdecode files, then you can use UU Undo for the Mac and WinCode to UUdecode in Windows.

.Z

A UNIX compression format. File Type: Binary
You can use WinZIP to decompress and view files with this extension, or try Stuffit Expander for the Mac. You can also use gzip to decompress, but not create, these file types.

.zip

A common compression standard for DOS and Windows that uses a DOS utility called PKZIP. File Type: Binary
These files can be decompressed on the PC with WinZIP. You can get copies for Windows 3.1 and Windows 95 (winzipXX.exe). You can also use Stuffit Expander for Mac or Windows.

Graphics Files

.gif

The most common graphics file format on the Internet, it stands for Graphics Interchange Format. File Type: Binary
If your browser does not have a built-in GIF viewer, then you can use Lview Pro (lviewpxx.zip) or PolyView (polyvxxx.zip) to view these graphics on a Windows PC. On the Mac, a shareware utility called GIF Converter can be used to view and modify GIFs.

.jpg/jpeg/jfif

A popular compression standard used for photos and still images. File Type: Binary
JPEG files can be viewed on any platform as long as you have a JPEG viewer. For the Mac, use JPEGView; for the PC, you can use Lview Pro or PolyView.

.tiff

A very large, high-resolution image format. File Type: Binary
Use JPEGView for the Mac and Lview Pro or PolyView for the PC.

All of the above graphics formats can be readily viewed, created, or manipulated with one or more commercially available graphics software programs like Photoshop or DeBabelizer for the Mac, and Photostyler or Photoshop for Windows.

Sound Files

.au/uLaw/MuLaw

The most common sound format found on the Web. File Type: Binary
Macs need Sound App to play this type of file; PCs can use Waveform Hold and Modify (whamxxx.zip) which provides support for a variety of formats, conversion between them, and file editing functions.

.aiff

Another fairly common sound format found on the Web. File Type: Binary
Although it is a Macintosh format, it can be used on other platforms as well. It requires the same programs as .au to play.

.mp3

The most popular file format on the Web for distributing CD-quality music. A 1 Mb files is equal to about one minute of music. File Type: Binary
This type of file requires an MP3 player, which is available for both Macintosh and Windows.

.ra

A proprietary audio format called RealAudio. Developed by a company called RealNetworks, RealAudio allows you to play sounds in real-time. File Type: Binary
This type of file requires a Real Player, which is available for both Macintosh and Windows.

.wav

The native sound format for Windows. File Type: Binary
On the Mac, you can use Sound App to play .wav files. For the PC, use aveform Hold and Modify or Goldwave to play these files. There's also a good program called Win Play! (wplnyxx.zip) that will play it, as well as other popular formats.

Video Files

.avi

The standard video format for Windows. File Type: Binary
These files need an AVI Video for Windows player (aviprox.exe).

.mov/.movie

The common format for QuickTime movies, the Macintosh native movie platform. File Type: Binary
You can use a number of applications to play .mov files including Sparkle or MoviePlayer on the Mac, and QuickTime for Windows.

.mpg/mpeg

A standard format for "movies" on the Internet, using the MPEG compression scheme. File Type: Binary
On the Mac, use Sparkle to play ,mpg files or to convert them to QuickTime movies. There are a variety of MPEG Players for Windows and an MPEG FTP Site that has a large collection of MPEG player resources for all platforms (Mac, Windows, and UNIX).

.qt

Another extension that denotes a QuickTime movie. File Type: Binary
Use the latest version (2.1) of Quicktime for the Mac.

Page Created by Shawn P. Rosler

Last Updated: 2.21.01