News.com has an interesting article on the
ENIAC. Read the article
here.
Be sure to listen to the MP3 provided at the link in the article that reads
Hear ENIAC programmer Jean Bartik explain how the computer was tested.
Confident programmers that were they had a "perfect program" used unit testing and break points for debugging way back then. And I've always heard that
debugging back in those days could be meant quite literally.