Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Well really its one of the first modern computers, the story isn't as clear cut as that. It was based on the American EDVAC (and earlier ENIAC).

It was the first operating computer I believe.
 
It was the first computer that could store a program in memory of some kind. Prevous computers had to have their programs either wired-in (essentially a single-purpose computer that could change its purpose with some re-wiring) or stored on some external memory of some kind (such as punch cards).
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.