CAOS (Cassette Aided Operation System)
my dad bought a computer called KC85/2 (a z80 clone) to my 5th birthday as a surprise when I remember right. Best birtdhay party ever

23 years ago
it's "base" was basic and we had a module in it which expanded the RAM with 64kb
[edit] best thing was that my parents recorded programs/games via radio onto cassette which we were able to run onto this machine (for free). that was awesome.[/edit]
after the german reunification he bought an Amiga500+ with Kickstart 2.04(?) on it + a 40MB external hdd which heralded "hammertime". I loved this Amiga. Great graphics (28 colors iirc) and awesome sound at this time (+500 of the best games at this time!). PC's dated years back, had 16 colors, pc speaker or even ugly monochrom ^^
then we got the 286 which later became my first PC. As I got it into my hands I started with MS-DOS 6.0 and Win 3.1 on it. had early a trident 8900c which supported 256 colors and also a creative 8 bit mono soundcard *oops sorry for off-topic*
those were times
