## Associated File Types

UNIX treats a file as a simple byte stream, and it is up to the program reading the file to impose a structure. This makes it difficult for UNIX vendors to offer functionality similar to the Macintosh Finder, where an application is associated with a file and is automatically launched when the file is selected. UNIX makes an attempt at this by using a "magic number" at the beginning of the file, but support for this is spotty and prone to error. Windows has traditionally used the three-character extension to tell the operating system which program should be used to open a file. This works most of the time, but there are problems with the limited number of possible extensions and conflicts when multiple programs are using the same extension.

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Last Updated: December 1, 1997