Karl Berry Olaf Bachmann and many others. The older DOS FAT file systems have severe limitations on file names. A file name may consist of no more than 8 characters, followed by an optional extension of no more than 3 characters. This is commonly referred to as an 8.3 file name.
Filenames are case insensitive.
There are a couple of filenames which are treated specially. These restrictions apply to DOS and also to at least some versions of Windows.