It doesn’t, though. QDOS was just a joke name used internally. The official name was 86-DOS, with DOS standing for Disk Operating System. It was named as a distinction for the fact it could load from disks (hard and floppy) and also that it supported disk filesystems. Previous generations of operating systems were loaded from tape or other supports and did not use files, so it was an important distinction to make.
It doesn’t, though. QDOS was just a joke name used internally. The official name was 86-DOS, with DOS standing for Disk Operating System. It was named as a distinction for the fact it could load from disks (hard and floppy) and also that it supported disk filesystems. Previous generations of operating systems were loaded from tape or other supports and did not use files, so it was an important distinction to make.
To add to this. DOSes existed going back to the 60s. IBM had DOSes for it’s System/360 mainframes back in '64.