With nearly 9,000 file extensions listed and 50 users browsing the site on a Saturday night, the Dot What!? claims to be the net's #1 file extension website. It offers visitors an opportunity to suggest additional file extensions and to add comments concerning their uses and associations.

While writing this column, I suggested .pl, an extension sometimes used for Perl scripts, and offered explanations for .cgi extensions. A review by a member of the Dot What!? team is necessary before updates and changes are posted.

For many file extensions, only an expansion of the extension itself is available. For .t2k files, for example, you will learn that these files are "Teach2000 Documents", but no other information is available. Over time, all of the nearly 9,000 file extensions may be well described, but for now, the "we do not have any further information" messages appear to dominate the site. Of course, just having some way to look up a file's extension you encounter can be extremely useful in determining how to work with it.

filext.com, another site devoted to file extensions, boasts what appears to be an even larger collection of file extensions. It offers 1,400 file extensions starting with the letter A. The site has, as of this writing, eight entries for .pl, including one for Perl scripts, but no detail on any of the eight types of files beyond the explanation of the file types. The site also has a large splattering of "Unknown Apple II File" extensions apparently discovered on a Golden Orchard Apple II CD ROM. While it's doubtful these entries will ever be expanded into useful descriptions of the related files, it's comforting to know someone is scavenging old media for evidence of bizarre file types.

There's also http://www.file-extensions.org, of course. It has six entries for .pl and a large collection of file extensions. It also sports a huge number of file extensions with "Unknown or unassigned file extension". In fact, the site seems to include an entry for every possible three-letter extension. Where else will you find an explanation of "z~^" as an unknown file extension? Not to mention "z~a" through "z~z","z~0" through "z~9", "z@@" and so on. You get the picture.

All of these sites boast thousands of file extensions and all have some way to search for a specific file extension or browse through a list of file extensions organized by their first letter. For now, the details on what the file extensions actually mean and what programs are required to work with them are skimpy. You might be better off googling the file extension you are trying to nail down, but you're likely to run into numerous conflicts before you find the one you want. I'd recommend bookmarking all of these sites and, over time, expect you will develop a preference. These sites might provide just the answer you need. Then again, they might not.

I found some of the sites to be overly cluttered, making it hard for me to locate the critical information once I drilled down to the right page. Still, it was helpful when a friend and colleague sent me an invoice in the form of a "wps" file. My Windows XP desktop only told me that the file required an "unknown application" to be opened. All three file extension web sites identified the file extension as belonging to MS Works Text Documents. Both Dot What!? and filext.com told me that I could open files of this type (and save in this format as well) using MS Word -- just what I needed to know.

The information on all of these sites will likely expand and become more useful and accurate over time. In any case, I have bookmarked all three in my "references" folder and expect they will prove useful on those rare occasions when I encounter a file with an unfamiliar extension and have no idea how to open and use it. Hopefully, I won't run into one of those "Unknown Apple II File" files!

ITworld.com

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