What's the oldest Windows OS you've used?

I was using DR DOS  before MS cloned it and did the 10% change to get away with it . And Geo Works windows before MS bought it to make windows 95  before MS had windows 1.0 .  Windows was first created by Xerox long before MS was even a company.

Oldest Windows OS was Windows 1.0, but used MS-Dos before that. You still had to know DOS to really use Windows, back in the day!

I'm also pretty sure I used Windows 1.0 in high school, and later 3.0 and 3.1 in the Navy before I switched over to IT and started working with NT. Then on to 2000, XP, and 7. Let's also not forget the various flavors of Windows Server.
I'm currently running 8.1 on my personal laptop but about to install 10.

The slide show forgot Windows ME and NT!

SGT (Join to see)
MS DOS baby!

I actually started in the AF in comms using MOD40/DSTE, not sure if there is an official OS for that. Then PC's with MSDOS 1.x and before Office, every thing was either command line or stand alone apps, like Lotus 123 (spreed sheet), Word Star and DEC PDP 11/84 running DEC OS.

I started out prior to MS-DOS. We had FORTRAN but I was learning Object Core Programming in college. Our computer had a whopping 1K of memory (wire wound around toroids). Windows started out as the first Graphical User Interface (GUI). We used to have to type in what we wanted using shorthand like "cd" for change directory, "del" for delete, etc.. With a mouse you could point and shoot what you wanted for programs. It was tough using windows as it barely worked on a 386SX machine. I upgraded my Toshiba 3200 gas plasma portable from 286 to do it. However all Windows did was point to the DOS programs. My hard drive was the limiter with 20MB which was the equivalent to 15 floppys at the time.
That said, I flew everywhere with that machine and a Diconix portable ink jet. As the R-2 I was able to do so much more work. I still have the Toshiba and it still runs. I just have to change out the CMOS battery every 7 years or so.

I know how to use binary code. It predated Windows.

Windows 10 still has many bugs that need to be worked out. The best version was XP professional. I've used Windows all back to ver 3.0

I've used DOS and Windows 1, as well as 3, 3.11, 98, 2000, XP, 7, 8, 8.1...