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?

  • 1
    Lol I always thought DOS meant "dirty operating system" Nov 26 '19 at 16:51
  • I always thought D(isk) was a strange way to start the acronym. I mean, the OS is operating so much more than the disk. "Disk operating system" sounds more like disk controller firmware than an actual operating system.
    – dwizum
    Nov 26 '19 at 19:20
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    @ThomasCook, given that MS-DOS/PC-DOS was based on QDOS, which was "Quick and Dirty OS", you were right. Nov 26 '19 at 19:53
  • Display On Screen
    – Aequitas
    Nov 27 '19 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). Dec 2 '19 at 23:26


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

Announced at the end of 1964 per Wikipedia.


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