I spent the summer of 1964 at Indiana University, where (among other things) I learned Fortran-II and wrote some programs for the quantum chemistry group. I was instantly hooked, and I've been having loads of fun with computers ever since. The system I used that summer was an IBM 709, the last vacuum tube computer that IBM made. Here are a couple photos of a 709 system. Note the blinding FLOPS ratings (and the price!).

[ Note (added 29 August 2006): I've been noticing that this page gets a lot more hits than I had anticipated. Most are the expected web-crawling bots (Googlebot, msnbot, Yahoo! Slurp, and many others). But many are actual humans, directed there by Google or some other search engine, to which they've provided “IBM” and “709” (and possibly other things) as search keywords; about one per day, on average. So ... If you're one of those people, I'd be curious to know why you're interested in the IBM 709. I know a few old-timers who remember using them in the early 60s. But what about the rest of you? Just interested in ancient computers? Something else? Drop me a note (mark@caltech.edu) if you feel like it. ]