DOS - back in 1985 Also bought a Commodore 64 that year and let the sales rep at Sears talk me into the state of the art tape backup system. A cassette player that connected to the C64 to save data. My, how the times have changed!
Mine was Apple II I can't remember what is the name of the program but it looks real bad in CGA monitor. The one I can remember was PC DOS and MS DOS.
Vic-20 BASIC in 1983/1984. Then a few Macs in the late 80s... Followed by the OS to rule them all.... GEM on an Atari 1040 STe. Still use it, and still love it. Any OS called "The Operating System" is cool in my book
That's quite new my friend I remembered camping out to get the first copies of Wndows 95, that was real madness.