This is enlightening. Growing up playing with Unix boxes (and XENIX, specifically, mostly writing shell scripts and playing in the filesystem) and programming MS-DOS in assembly I could often see strange parallels between how stuff worked in MS-DOS and his stuff was in Unix. I just assumed MSFT programmers had used Unix at some point and wanted to lift features and idioms from it to use in DOS. It never occurred to me, knowing XENIX was a MSFT-licensed Unic derivative, that there might be more direct inspiration in that vague Unix "flavor" in DOS.

I never did any CP/M programming, so the whole FCB-based file manipulation API in MS-dos just seemed like strange old cruft to me. Had I been exposed to CP/M the Unix inspiration behind the handle-based API would have been a lot more apparent. (I got in about the MS-DOS 3.3 timeframe...)

What a strange world it would have been in MSFT got IBM to buy into the Unix path separator.