**** COMMODORE 64 BASIC V2 ****
It was a 64K RAM system with 38,911 BASIC bytes free, of course.
I got a C64 on my 8th birthday (1983), but my dad was a teacher and before the C64 he brought home an Atari 400 over the summer when I was 5 and an Atari 800 with the floppy drive when I was 6. When I was 6 or 7 we had a Timex Sinclair for awhile, but I think we took it back. My neighbor had a TRS-80, and I used it to figure out annoying things to do with the display computers at Radio Shack.
I don't know if they even had a name for the C64 OS. It was just "the OS" and it was built into ROM. Computers before the Mac were more like a BIOS that took you directly to a BASIC shell. It seems strange to even call it an OS. It wasn't CP/M -- that was something different. The C64 didn't have CP/M (the C128 had a CP/M compatible mode that nobody used, though).
The first graphical OS I used was probably my friend's dad's Mac in 1985, but I did get GEOS for the C64 in 1986.
I got a Tandy 1000 in 1987. I think that was right about when DOS 3 came out. We eventually upgraded it to 640K and added a 3.5" floppy drive, but still no hard drive. The Tandy 1000 was indestructible. It was a 7 MHz 8088 that just wouldn't die. It was a really cool-looking computer at the time. The original IBM PC always had a greenish screen that made it look really low-tech, and the Mac had a nice black & white screen, but it was stilly really grayich. The Tandy came with a really good monitor that was true white on solid black. At the time it was almost futuristic.
I got a 386SX-16 in '89 or '90. That thing actually had a 100MB hard drive. I spent most of my time dialing into BBS's and downloading McHenry boobie pictures. Still just used DOS.
Then I got a Pentium 90 in 1994 when I went to college, but that's not the stone age anymore, so it's not very interesting to talk about. I still remember thinking Windows for Workgroups 3.11 really sucked, but you had to use it and this little Trumpet WinSock program to get on the Internet with a PC. Well, you didn't have to, but there just weren't too many DOS programs to compete with the Windows versions of Mosaic, WS-FTP and Eudora, which is pretty much all you used when you were on the net.