The rise and fall of IBM's 4 Pi aerospace computers: an illustrated history

Summary

The morning of April 12, 1981, 20 years to the day after Yuri Gagarin became the first person in space, the Space Shuttle thundered into the Florida sky. Commander Young and Pilot Crippen were at the controls as the Shuttle ascended on its first flight. But the launch, like much of the flight, was really under the control of four computers in the avionics bays one deck below the crew. A fifth computer stood ready to take over in case of a catastrophic computer malfunction. These computers, Model AP-101B, were part of IBM's System/4 Pi family. The Space Shuttle AP-101B computer. This unit flew on multiple flights, including STS-38 (1990) and STS-40 (1991). Photo courtesy of RR Auction. Introduced around 1967, the System/4 Pi family was a line of compact, powerful computers designed for avionics roles. The military used these computers in everything from the F-4 fighter and B-52 bomber to submarine sonar systems and the Harpoon anti-ship missile. Other computers in the System/4 Pi family played more peaceful roles in the development of GPS and fly-by-wire flight controls. In space, System/4 Pi computers controlled Skylab, the first American space station, as well as Spacelab, the reusable laboratory flown by the Space Shuttle. Despite the important roles of System/4 Pi computers, information on them is hard to obtain—Wikipedia entirely omits the CC, SP, and ML models.1 However, I received a stack of 4 Pi marketing brochures and articles, so I can now fill in many gaps in the history of System/4 Pi. The first generation The IBM System/360 line of mainframes was introduced in 1964. System/360 revolutionized the computer industry with the concept of one family of computers for all applications: business and scientific. The name symbolized that System/360 covered the full 360º of applications. The 4 Pi name extended this idea to applications in the 3-dimensional world: 4π is the number of steradians making up a full sphere. As IBM put it, "System/4 Pi also fills a sphere—...