AP-101
The IBM AP-101 is a computer used in avionics, most notably in the U.S. space shuttle, but also in the B-52 bomber among others. When it was designed, it was a high-performance pipelined processor with core memory. In 2003, its specifications are exceeded by many microprocessors.The AP-101 has the same general architecture as the System 360 and 4Pi computers. It has 16 32-bit registers, and uses a microprogram to define an instruction set of 154 instructions. Originally only 16 bits were available for addressing memory, later extended with four bits from the program status word register.
It is built using TTL integrated circuits. The main memory was originally core memory, but the AP-101S upgrade in the early 1990s used semiconductor memory.
A shuttle uses five AP-101s as "general-purpose computers" (GPCs). Four operate in sync, for redundancy, while the fifth is a backup running software written independently. The shuttle software is written in H/A>, a special-purpose high-level language.
AP-101s used by the US Air Force are mostly programmed in JOVIAL.
