MS-DOS a.k.a. PC-DOS nee QDOS, was commonly just referred to as DOS. But 'disk operating system' is a very obvious acronym; there must have been previous operating systems so called.

What was the first operating system called DOS?

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    Lol I always thought DOS meant "dirty operating system" Commented Nov 26, 2019 at 16:51
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    @ThomasCook, given that MS-DOS/PC-DOS was based on QDOS, which was "Quick and Dirty OS", you were right. Commented Nov 26, 2019 at 19:53
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    Display On Screen
    – Aequitas
    Commented Nov 27, 2019 at 0:23
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    @dwizum - it's not that the System is Operating the Disk, it is that the Operating System is Disk-based, in contrast to the many predecessors which were not disk-based (and probably ran on computers which had no disks - because disks were expensive luxuries).
    – dave
    Commented Dec 2, 2019 at 23:26
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    @RayButterworth - well, that's another question (maybe you should post it?). Who came up with the name "PC-DOS" - IBM or Microsoft? If IBM, I think it most likely that the men in suits named PC-DOS in the same way that they had named DOS/360,, DOS/VS, DOS/VSE -- in which case it's D for Disk.
    – dave
    Commented Dec 2, 2019 at 23:30

1 Answer 1



(As distinct from TOS/360, the tape OS)

Announced at the end of 1964 per Wikipedia.

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    So, "DOS: The Original Series" aka TOS :D Commented Nov 26, 2019 at 19:05
  • That's interesting! Etymonline which in my experience as a language enthusiast is actually pretty good, lists the first use of DOS as 1967. Commented Jun 8, 2022 at 4:46
  • "Announced" is not the same as "available to customers". The Wikipedia link says delivered in June 1966, so there's still a slight discrepancy.
    – dave
    Commented Jun 8, 2022 at 12:08

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