Microsoft made its name in the mid-to late-1970s, being market leaders for interpreters and compilers (the one thing they still do halfway decently, if you ask me). But William Gates was in the business by 1971, helping a computer company fix its security holes in return for CPU time.
Now there's an irony if I ever saw one -- anybody involved with Microsoft even _trying_ to resolve security problems. Normally these days, they only multiply them while proclaiming they never existed.
By the way, you don't need an integrated circuit -- or a microprocessor -- to have a programmable computer (i.e., one that can run software). See the Zuse Z3, built in 1941, long before even the basis for integrated circuits (the transistor) had been developed. It was fully programmable and eventually found to be Turing complete. Yes, there was software written for it... which worked as advertised, so obviously Microsoft didn't have their hands on it back then.
But sarcasm aside, commercial software development has been going on since the late 1950s at least, when banks and insurances got hooked on basement-sized pocket calculators. Microprocessors just plain never were necessary to run software.
Back to work here... may Ballmer ball MS up against a wall so I can be rid of all the idiots running their Windows installations against the wall at full tilt with me being the one who has to fix their booboos.
Oh, shucks, may Steve B. throw himself out of a window instead of chairs at employees for a change. I'm just sick and tired of having to clean up the messes Microsoft made and can't be arsed to fix.
-- sorry, go ahead, I'm wearing my Asbestos tonight, so flame away. Just had a lot of Vista today... too much, in fact. Plus some XP SP3 and w2k and "server" 03.