[jdietrich]

Architecturally, the Z3 and the Manchester Baby are very different. The Z3 is essentially a programmable calculator, lacking random-access memory or conditional branching. It's just barely Turing complete, but this was only discovered in 1998 after a very clever analysis by Raúl Rojas.

The Manchester Baby is small, slow and primitive, but it's also fundamentally modern, implementing a proper von Neumann architecture. It had a much more primitive arithmetic unit than the Z3 (capable only of subtraction and negation), but it had an instruction set that would be familiar to a modern programmer.

Zuse didn't know that he had built a Turing-complete computer. He was a practical man and built a practical machine for performing useful calculations. The Manchester Baby was explicitly built as a general-purpose computer. It was in many ways less useful than than the Z3, but it was a far more significant advance. Although Kilburn, Williams and Tootill knew nothing of the work that had been done at Bletchley Park, they were guided by people who did.