Code: The Hidden Language of Computer Hardware and Software, 2nd Edition

Chapter Fifteen

Is This for Real?

In the previous chapter, you saw how you can wire relays together to make a 1-bit adder and then combine eight of them to add two bytes together. You even saw how those 8-bit adders could be cascaded to add even larger numbers, and you may have wondered, Is this really how computers add numbers?

Well, yes and no. One big difference is that computers today are no longer made from relays. But they were at one time.

In November 1937, a researcher at Bell Labs named George Stibitz (1904–1995) took home a couple of relays used in telephone switching circuits. On his kitchen table, he combined these relays with batteries, two lightbulbs, and two switches he made from strips of metal cut from tin cans. It was a 1-bit ...