CertiGuide to A+ (Operating Systems)  9  Chapter 0011:  DOS       9  IV  COMMAND.COM and Basic DOS Commands

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The lineage of DOS dates back to the ‘70’s. This heritage explains why there's a limit of 8 characters followed by the dot with a maximum of 3 characters for the extension.

The 8-character limit no longer exists in Windows, but it is definitely a part of heritage on the DOS platforms, and references to it are still present on many versions of Windows. For example, the DIR command on many versions of Windows will still display two name columns in its directory listings – the first column, a shorter name that Windows has made up, like “Progra~1,” to make the user’s file name look like one of these 8.3 format filenames, and the last column, the original long name for the file or folder, like “Program Files”.

Extensions can be anything you want, or even none at all. The wise geek would follow commonly accepted conventions, as we discussed earlier. Some of the most common ones are:

• .exe: Executable
  
  
• .com: Command
  
  
• .txt: Text
  
  
• .doc: Document
  
  
• .bat: Batch file
  
  
• .sys: System extension (driver)
  
  
• .bak: Backup
  
  
• .ini: Initialization
  
  
• .inf: Information (system setup)
  
  
• .reg: Registry
  
  
• .pdf: Acrobat (Adobe)
  
  
• .bmp: Bitmap graphic (paint)
  
  
• .tif graphic image

This list is by no means conclusive. If you don’t follow the common conventions, you may have a tough time getting a data file to work with an associated program.

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