A lot vs. Alot: 9 Grammatical Pitfalls
file system, filename extension
A common shorthand for the limits on filename length imposed by the file system used by MS-DOS and Microsoft Windows - at most eight characters, followed by a ".", followed by a filename extension of at most three characters.
Windows 95 supports long filenames by using multiple directory entries per file. The extra entries are hidden. It also automatically derives an 8.3 name for each file for backward compatibility so that older versions of DOS can still access the file.