Despite their excitement and impatience, Eckert and Mauchly started work cautiously. They knew something that none of their benefactors did: Although they had the basic outline of what they were going to build, they had not worked out exactly how they were going to create it. And unlike Aiken, who had all those IBM engineers working to make his concept a reality, they were on their own.
ENIAC, they had decided, would have three main parts. First, there would be self-contained machines to handle the math operations: units built for addition, a highspeed multiplier, and a box wired to handle division and square roots. Second, there would be memory units to store numbers and instructions. Most of these would be electronic, since numbers had to move quickly through the machine. But some would be big mechanical panels with