Atari 800, back in 1983. Which I bought because of 'Star Raiders' - which had what is still one of the best gameplays I've seen. I even got into programming the thing in 6502 assembly language, which I don't think I could do again! Subsequently an 800XL, then an Atari ST, then a variety of PCs. Who knows? Once day maybe I'll get a Mac...

Steve