How to identify file types after downloading from the Internet

How Does Uploading and Downloading Work?

Typically, downloading is the process of accessing and saving files to your computer from another computer. If you wanted to send something from your computer to another computer, the process would be referred to as "uploading." Most of the time, though, you will be on the receiving end, downloading.

For instance, when you access a web page, you are actually downloading the page of text and all the associated graphics from a server. In fact, when you receive electronic mail - email - that contains an attachment, you have actually downloaded both the email message and the attachment. The files you download can be documents or programs that let you:

Update your computer's software
See graphics
Hear sounds, music
See video pictures
Read text

Downloading is the process that creates your own copy of a file by copying it from another computer to yours. Once a file is downloaded, it is a simple matter to use it or change it. First you must identify the file type (also called its format).

Identifying File Types

In the Windows environment, the file extension lets your computer know which program opens that file. This is the piece of text at the end of a file name, preceded by a period, which identifies the file type. For example, the .txt extension means the file is a plain text file. It is also sometimes referred to as an ASCII file. Any program that can read ASCII text can open this file and read it. Most file extensions are three or four characters long. On some operating systems, such as UNIX, they are four characters. Normally, each file has only one file extension, but some operating systems like UNIX and most Windows programs allow multiple extensions as well as extensions with more than three characters.

For the most part, on the Internet, every file has a three or four character extension. Macintosh files do not require a file extension and instead have an identifier built into the file that is visible only to the computer. Mac files on the Internet, however, do have extensions, like .sea. Most image files end with .jpg and .gif. The former stands for JPEG, which is a popular compression standard for photos and other still images. The latter extension stands for Graphics Interchange Format, a standard that was developed by CompuServe in the late 1980s. Both of these graphics formats can be used on PCs, Macs, or UNIX machines as long as viewing software has been installed. Also, your word processor can work with these files using the "Insert Picture From A File" option in Microsoft Word or "Insert Graphics From File" in WordPerfect.

Popular extensions for video files are .avi for the PC, .mpg (short for MPEG), .mov and .qt for QuickTime movies. Sound files come in .aiff for Macintosh; .au for Mac and UNIX; .wav for the PC; and .ra for Real Audio, which is a Web proprietary system for delivering and playing real-time audio.

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