[mooism2]

Windows/MS-DOS had file extensions (which it inherited from CP/M) before it had directories and directory separators.

Did CP/M and Unix independently come up with file extensions with a dot separator, or did they acquire it from the same source? I'm dimly aware of other operating systems that use(d) a different character (AS/400?), but it's outside my ken.

[ja27]

I believe Microsoft's file extensions and the 8.3 naming scheme are descended from Digital's 6.3 naming in VMS, RT-11, etc. DEC even used a number of the same extensions: EXE, COM, OBJ. Not sure where they came from prior to that. I don't think IBM used file extensions like that in System/360, System/32, or anything prior to PC-DOS. From what I can tell, Burroughs and Univac didn't use them either.