The first version of DOS that I used was 3.2. I think it was MS, but I might have been PC DOS. It ran on a Source One Systems XT clone with an 8088-2 @ 8MHz, 640KB RAM, a 360KB 5.25" fdd, a 20MB MFM hdd, and CGA graphics.
Now I have DOS 6.0 or 6.22, I don't remember which, installed on it and still use it some.