4.5. Working with 8.3 File Naming

Early PC systems used a standard naming convention for files called the 8.3 format. This format allowed eight characters for the filename and three characters for the file type or extension. Certain file extensions told the operating system to immediately start executing a file (for example, .bat, .com, and .exe).

Modern systems have expanded the 8.3 format to allow longer and user-friendlier filenames. They still maintain the file extension type and hide it from the user.

If a file type is indicated—for instance, a filename has a .jpg extension—the system automatically opens the program that has been registered to be associated with the file. Table 4.1 shows some of the common file types used in PC systems today.

Many operating systems, including Windows environments, hide the file extension from the user. A user may receive a file named mycatspicture and assume that it's a JPEG or other picture. Unfortunately, the actual file type isn't usually shown to the user when they contemplate opening it. If the file is an executable or a script, it will start executing using the appropriate language or command processor. If this file is a Trojan horse, a worm, or some other form of malicious code, the system has potentially been compromised.

Files can even appear to have more than one filename extension. A file may indicate that it's mycatspicture.jpg when it's actually mycatspicture.jpg.exe. This file will start executing when it's opened and may expose the system to malicious code.

From a user's perspective, the simpler things are, the easier they are to work with. However, from an administrator's perspective, you want to know as much as you can. Windows XP, like its most recent predecessors, by default hides known file extensions as well as certain files and folders.