June 10th, 2009

Why does MS-DOS use 8.3 filenames instead of, say, 11.2 or 16.16?

Raymond Chen
Raymond Chen

When I discussed years ago why operating system files tend to follow the old 8.3 file name convention, I neglected to mention why the old MS-DOS filename convention was 8.3 and not, say, 11.2 or 16.16.

It’s a holdover from CP/M.

As I noted when I discussed the old MS-DOS wildcard matching rules, MS-DOS worked hard at being compatible with CP/M. And CP/M used 8.3 filenames.

Why did CP/M use 8.3 filenames? I don’t know. There’s nothing obvious in the CP/M directory format that explains why those two reserved bytes couldn’t have been used to extend the file name to 10.3. But maybe they figured that eight was a convenient number.

Category
Old New Thing
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History

Author

Raymond Chen

Raymond has been involved in the evolution of Windows for more than 30 years. In 2003, he began a Web site known as The Old New Thing which has grown in popularity far beyond his wildest imagination, a development which still gives him the heebie-jeebies. The Web site spawned a book, coincidentally also titled The Old New Thing (Addison Wesley 2007). He occasionally appears on the Windows Dev Docs Twitter account to tell stories which convey no useful information.

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