Different Types of Files There are five main categories of files that you will find on the Internet. They are identified by their extension - the three letters after the dot after the filename.
Text Files (.txt)
These are the files that contain text, or writing. It may be text you can read or source code for a computer program. Text files can even be data files for other programs.
Executable Files (.exe, .com or .dll)
These are program files. You can run the program on your computer.
Executable files are specific to an operating system - a Mac file will not run on Windows, and vice versa. The most common executable files on the Internet are for DOS and Windows. You run them like any other DOS or Windows program - double click on the filename etc.
Compressed Files
A compressed file is a file that has been stored in a special way so it takes up less space on the computer. Compressed files can be called Archived files, ZIP files, SIT files, or other names. You need to de-compress a compressed file before you can use it. Once it is de-compressed, a compressed file can be any of the other four types.
Archive files are a lot of files that have been put together in one package - a multifile file. You need to unarchive these files before you can use them. You do this using an unarchiving program.
Zip files (.zip) and StuffIt files (.sit) are discussed above. They have their compression and archiving done together, by the one program.
Graphics, Audio and Video Files
These files contain pictures and sound in a form that computers can read.
Graphics files are usually in the formats GIF, PNG or JPEG. There are many other graphics formats around - PCX (DOS format used by many paint programs), TIFF, PICT (common on Macs as they have built in support for it), BMP (bitmap files - the native windows format) to name a few. GIF files have the extension .gif. They have no more than 256 colours and a resolution that matches PC screens - 640x480, 1024x768 etc. The two main browsers can display GIF files using File/Open. PNG files is the patent free version of GIF. JPEG is a format for photos only. The two main browsers can display JPEG files using File/Open. Audio files are usually in the formats WAV or RAM. You can download an audio file, and then play it, or play the file as you download it. To play a downloaded file, you need a sound player, which comes with the latest web browsers.
To play the file as you download it - called streaming audio - you need a plug in to your browser. Most streaming audio files are in RA or RAM format, so you need a RealPlayer plug-in. You can download this plug -in from http://www.real.com or http://www.tucows.com.
Video files are digitised movies. The standard format is MPEG. You need a fast computer to display these in real-time. Other formats exist and can be viewed using plug-ins to your web browser.
Data Files
These are any files that do not fit in the above categories. An example would be a file formatted for a word processor, such as WordPerfect. Such files can usually be viewed in a text processor, such as Notepad in Windows 95. Microsoft has a free program that reads Word files at http://office.microsoft.com/downloads/9798/wd97vwr32.aspx.
A Note on Mac Files
Mac files usually come in three parts - the data file, the resource file and the information file. These are known as forks - data fork etc. When you upload a file from a Mac it often appears as these three different forks - the data fork has the extension .data, the resource fork has the extension .resc, and the information fork has the extension .info. Various schemes exist to archive these files in one package for sending over the Internet.