Q: Can more than one program use the same file extension?
A: There are tens of thousands of computer programs available. This means there are also tens of thousands of file extensions. Because there is no centralized database for file extensions, many times these file extensions overlap. That is, one file extension might be used by multiple programs.
The correlation between a file extension and the program that uses it is called a "file association." Therefore, an extension that is used by more than one software program has multiple file associations. While most common file extensions, such as .TXT, .JPG, and .MP3 are associated with distinct file types, less popular extensions are more likely to have multiple file associations. Some examples include .ART, .PRF, .KEY, and .VC4. Fortunately, files also have internal data that defines the format of the file, which can help the computer choose the correct program to open them with.
It would be ideal if each file extension had only one file association. But since there was no central file extensions registry for many years, developers could choose whatever file extensions they want for their programs' files. Fortunately, FileInfo.com now serves as the central file extensions database. By checking FileInfo.com for existing extensions, developers can be sure they they choose new extensions for their file types.
Updated: June 13, 2011