Reverse engineering circuitry in a Spacelab computer from 1980
Summary
Ken Shirriff reverse-engineers the Spacelab Mitra 125 MS ALU boards, detailing how a 16-bit minicomputer achieved 32-bit operations using multiple TTL '181 chips, multiplexers, and carry-lookahead logic. The article provides historical context on the Spacelab computer, its modular ALU design across three boards, and the transition to IBM's AP-101SL computers.