Ken Shirriff writes about the Arma Micro Computer from 1962, older than the machines usually named as the first microcomputer. This 20-pound transistorized computer was built for aerospace work like navigation and engine control, with a 22-bit serial architecture and a small instruction set that still had some complex operations. Its storage used transfluxors, which can be read without destroying what’s stored in them, and that helped its reliability in aerospace use. Because it was built from discrete components, it doesn’t meet the modern definition of a microcomputer.
Full article: Ken Shirriff’s blog.