The rise and fall of IBM's 4 Pi aerospace computers: an illustrated history
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- #Space Shuttle Computers
- #IBM System/4 Pi
- #Avionics History
- The Space Shuttle's maiden flight on April 12, 1981, was controlled by IBM System/4 Pi computers, specifically the AP-101B model.
- The System/4 Pi family, launched in 1967, was IBM's line of compact avionics computers used in military and space applications, including fighters, bombers, missiles, and spacecraft like Skylab.
- First-generation models included the TC (Tactical Computer) with magnetic core memory, used in Skylab; the CP (Customized Processor) for navigation and weapons; and the EP (Extended Performance), compatible with IBM System/360.
- Advanced System/4 Pi models, introduced in 1970, featured improved performance with Medium-Scale Integration (MSI) chips. The AP series powered the Space Shuttle, with the AP-101B using quadruple redundancy and a backup computer.
- The AP-101S, an upgrade for the Shuttle, combined the CPU and I/O into one box, tripled speed to 1.27 MIPS, and used semiconductor memory with error-correcting codes for radiation resistance.
- Other lines included the SP (Subsystem Processor) for displays and missiles, the CC (Command and Control) for AWACS aircraft with bubble memory, and the ML-1 using Large-Scale Integration (LSI) chips.
- The AP-102, popular in the 1980s, adopted VLSI technology and the MIL-STD-1750A instruction set, later enhanced with VHSIC chips for radiation hardening and higher performance.
- IBM ended the System/4 Pi line in 1994 by selling its Federal Systems Division, but the computers exemplified rapid technological progress from TTL and core memory to CMOS and semiconductor memory.