IBM AP-101
Encyclopedia
The IBM AP-101 is an avionics
computer
, used most notably in the U.S. Space Shuttle
, but since also in the B-52
and B-1B bombers and the F-15
fighter, among others. When it was designed, it was a high-performance pipelined processor with core memory. While its specifications are exceeded by many modern microprocessor
s, it was considered high-performance for its era as it could process 480,000 instructions per second
(compared to the 7,000 instructions per second of the computer used on Gemini spacecraft). It remains in service (formerly on the space shuttle) because it works and is flight-certified, whereas a new certification would be too expensive. The Space Shuttle AP-101s were augmented by glass cockpit
technology.
The AP-101, being the top-of-the-line of the System/4 Pi
range, shares its general architecture with the System/360
mainframe
s. 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 this was extended with four bits from the program status word
register, allowing a directly addressable memory range of 1M locations.
The original AP-101 was built using TTL
integrated circuit
s. The main memory was originally core memory, but the AP-101S upgrade in the early 1990s used semiconductor memory
.
The space shuttle used 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 was written in HAL/S
, a special-purpose high-level language, whereas AP-101s used by the US Air Force are mostly programmed in JOVIAL, such as the system found on the B-1B Lancer bomber.
Avionics
Avionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...
computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
, used most notably in the U.S. Space Shuttle
Space Shuttle program
NASA's Space Shuttle program, officially called Space Transportation System , was the United States government's manned launch vehicle program from 1981 to 2011...
, but since also in the B-52
B-52 Stratofortress
The Boeing B-52 Stratofortress is a long-range, subsonic, jet-powered strategic bomber operated by the United States Air Force since the 1950s. The B-52 was designed and built by Boeing, who have continued to provide maintainence and upgrades to the aircraft in service...
and B-1B bombers and the F-15
F-15 Eagle
The McDonnell Douglas F-15 Eagle is a twin-engine, all-weather tactical fighter designed by McDonnell Douglas to gain and maintain air superiority in aerial combat. It is considered among the most successful modern fighters with over 100 aerial combat victories with no losses in dogfights...
fighter, among others. When it was designed, it was a high-performance pipelined processor with core memory. While its specifications are exceeded by many modern microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s, it was considered high-performance for its era as it could process 480,000 instructions per second
Instructions per second
Instructions per second is a measure of a computer's processor speed. Many reported IPS values have represented "peak" execution rates on artificial instruction sequences with few branches, whereas realistic workloads typically lead to significantly lower IPS values...
(compared to the 7,000 instructions per second of the computer used on Gemini spacecraft). It remains in service (formerly on the space shuttle) because it works and is flight-certified, whereas a new certification would be too expensive. The Space Shuttle AP-101s were augmented by glass cockpit
Glass cockpit
A glass cockpit is an aircraft cockpit that features electronic instrument displays, typically large LCD screens, as opposed to the traditional style of analog dials and gauges...
technology.
The AP-101, being the top-of-the-line of the System/4 Pi
System/4 Pi
The IBM System/4 Pi is a family of radiation hardened avionics computers used, in various versions, on the B-52 Stratofortress bomber, the F-15 Eagle fighter, E-3 Sentry, NASA's Skylab space station, MOL, and the Space Shuttle, as well as other aircraft. It descends from the System/360 mainframe...
range, shares its general architecture with the System/360
System/360
The IBM System/360 was a mainframe computer system family first announced by IBM on April 7, 1964, and sold between 1964 and 1978. It was the first family of computers designed to cover the complete range of applications, from small to large, both commercial and scientific...
mainframe
IBM mainframe
IBM mainframes are large computer systems produced by IBM from 1952 to the present. During the 1960s and 1970s, the term mainframe computer was almost synonymous with IBM products due to their marketshare...
s. It has 16 32-bit
32-bit
The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory....
registers
Processor register
In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
, and uses a microprogram to define an instruction set
Instruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
of 154 instructions. Originally only 16 bits were available for addressing memory; later this was extended with four bits from the program status word
Status register
A status register or flag register is a collection of flag bits for a processor. An example is the FLAGS register of the x86 architecture....
register, allowing a directly addressable memory range of 1M locations.
The original AP-101 was built using TTL
Transistor-transistor logic
Transistor–transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor–transistor logic because both the logic gating function and the amplifying function are performed by transistors .TTL is notable for being a widespread...
integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s. The main memory was originally core memory, but the AP-101S upgrade in the early 1990s used semiconductor memory
Semiconductor memory
Semiconductor memory is an electronic data storage device, often used as computer memory, implemented on a semiconductor-based integrated circuit. Examples of semiconductor memory include non-volatile memory such as Read-only memory , magnetoresistive random access memory , and flash memory...
.
The space shuttle used 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 was written in HAL/S
HAL/S
HAL/S is a real-time aerospace programming language, best known for its use in the Space Shuttle program. It was designed by Intermetrics in the 1970s for NASA. HAL/S is written in XPL, a dialect of PL/I....
, a special-purpose high-level language, whereas AP-101s used by the US Air Force are mostly programmed in JOVIAL, such as the system found on the B-1B Lancer bomber.
Papers
- Norman, P. Glenn, IBM Corp. (1987). The new AP101S General-Purpose Computer (GPC) for the Space Shuttle. IEEE Proceedings, Volume 75, pp. 308–319, 1 March 1987.
- Vandling, Gilbert C. Organization of a Microprogrammed Aerospace Computer. Computer Design, pp. 65–72, February 1975.