Ken Shirriff provides another excellent post, this time on the computer used on Spacelab back from 1980. Spacelab was a reusable laboratory that could be carried in the cargo bay of the Space Shuttle, providing lab space for astronauts and experiments. Spacelab was controlled by a French-built minicomputer, called the Mitra 125 MS. Unlike modern computers, this computer didn’t contain a microprocessor chip. Instead, its 16-bit processor was constructed from several boards of chips. In this article, I reverse-engineer one of the processor boards, shown below, part of the computer’s Arithmetic/Logic Unit (ALU). The Spacelab computer provides an interesting look at how computers were built before microprocessors took over. The components of a computer, such as the ALU, registers, and control circuitry, were constructed from simple chips. Since each chip didn’t do much, the computer required 36 boards full of chips. Even so, the computer was compact enough to go into space.…