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The IBM System/4 Pi is a family of avionics computers used, in various versions, on the F-15 Eagle fighter, E-3 Sentry AWACS, Harpoon Missile, NASA's Skylab, MOL, and the Space Shuttle, as well as other aircraft. Development began in 1965, deliveries in 1967. [1] They were developed by the IBM Federal Systems Division and produced by the Electronics Systems Center in Owego, NY. [2]
It descends from the approach used in the System/360 mainframe family of computers, in which the members of the family were intended for use in many varied user applications. (This is expressed in the name: there are 4π steradians in a sphere, just as there are 360 degrees in a circle. [3] ) Previously, custom computers had been designed for each aerospace application, which was extremely costly.
In 1967, the System/4 Pi family consisted of these basic models: [4] [5]
Model | ISA (instructions) | Performance (IPS) | Weight (pounds) |
---|---|---|---|
TC | 54 | 48,500 | 17.3 pounds (7.8 kg) |
CP | 36 | 91,000 | 80 pounds (36 kg) |
CP-2 | 36 | 125,000 | 47 pounds (21 kg) |
EP | 70 | 190,000 | 75 pounds (34 kg) |
The Skylab space station employed the model TC-1, [17] which had a 16-bit word length and 16,384 words of memory with a custom input/output assembly. Skylab had two, redundant, TC-1 computers: a prime (energized) and a backup (non energized.) There would be an automatic switchover (taking on the order of one second) to the backup in the event of a critical failure of the prime. [18] A total of twelve were delivered to NASA by 1972. Two were flown on Skylab in 1973-1974; the others were used for testing and mission simulators. [19] The software management effort was led by Harlan Mills and Fred Brooks. The Skylab flight software development process incorporated many lessons learned during the IBM System/360 Operating System project, as described in Brooks' 1975 book The Mythical Man-Month . [19]
The AP-101, being the top-of-the-line of the System/4 Pi range, shares its general architecture with the System/360 mainframes. [19] It is a repackaged version of the IBM Advanced Processor-1 (AP-1) [20] used in the F-15 fighter. [19] The AP-1 prototypes were delivered in 1971 and the AP-101 in 1973. [21] It has 16 32-bit registers. 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. This avionics computer has been used in the U.S. Space Shuttle, the B-52 and B-1B bombers, [19] and other aircraft. It remained in service on the Space Shuttle because it worked, was flight-certified, and developing a new system would have been too expensive. [22]
There were a number of variants of the AP101. The Offensive Avionics System, a retrofit update of the B-52, contains two AP-101C computers. [23] The AP-101C prototypes were delivered in 1978. [21] The B-1B employs a network of eight model AP-101F computers. [24] The Space Shuttle used two variants of the AP-101: the earlier AP-101B and the upgraded AP-101S. The AP-101B was used for a series of Approach and Landing Tests in 1977. The first ascent to orbit was in 1981. The AP-101S first launched in 2000.
Each AP-101 on the Shuttle was coupled with an input-output processor (IOP), consisting of one Master Sequence Controller (MSC) and 24 Bus Control Elements (BCEs). The MSC and BCEs executed programs from the same memory system as the main CPU, offloading control of the Shuttle's serial data bus system from the CPU. The AP-101B originally used in the Space Shuttle had magnetic-core memory. The upgrade to the AP-101S in the early 1990s replaced the core with semiconductor memory and reduced the size from two to one chassis. [25] It was augmented by glass cockpit technology. Both variants use a microprogram to define the instruction set architecture. The early AP-101 variants used IBM'S Multipurpose Midline Processor (MMP) architecture. [26] The AP-101B microprogram implemented MMP with 154 instructions. The AP101S could operate with a backwards compatible MMP with 158 instructions or the MIL-STD-1750A architecture with 243 instructions. [25] It was based on the AP-101F used in the B-1B. The AP-101S/G was an interim processor. The AP-101B performance was 0.420 MIPS, while the AP-101S was 1.27 MIPS. [25] James E. Tomayko, who was contracted by NASA to write a history of computers in spaceflight, has said: [27]
"It was available in basically its present form when NASA was specifying requirements for the shuttle contracts in the 1970s. As such, it represents the first manned spacecraft computer system with hardware intentionally behind the state of the art."
The Space Shuttle used five AP-101 computers as General-Purpose Computers (GPCs). Four operated in sync, for redundancy, while the fifth was a backup running software written independently. The Shuttle's guidance, navigation and control software was written in HAL/S, a special-purpose high-level programming language, while much of the operating system and low-level utility software was written in assembly language. AP-101s used by the US Air Force are mostly programmed in JOVIAL, such as the system found on the B-1B bomber. [28]
The AP-102 variant design began in 1984. It is a MIL-STD-1750A standard instruction set architecture. It was first used in the F-117A Stealth Fighter. It was upgraded to the AP-102A in the early 1990s. [29]
IBM mainframes are large computer systems produced by IBM since 1952. During the 1960s and 1970s, IBM dominated the computer market with the 7000 series and the later System/360, followed by the System/370. Current mainframe computers in IBM's line of business computers are developments of the basic design of the System/360.
The IBM System/360 (S/360) is a family of mainframe computer systems announced by IBM on April 7, 1964, and delivered between 1965 and 1978. System/360 was the first family of computers designed to cover both commercial and scientific applications and a complete range of applications from small to large. The design distinguished between architecture and implementation, allowing IBM to release a suite of compatible designs at different prices. All but the only partially compatible Model 44 and the most expensive systems use microcode to implement the instruction set, featuring 8-bit byte addressing and fixed-point binary, fixed-point decimal and hexadecimal floating-point calculations.
Skylab was the United States' first space station, launched by NASA, occupied for about 24 weeks between May 1973 and February 1974. It was operated by three trios of astronaut crews: Skylab 2, Skylab 3, and Skylab 4. Operations included an orbital workshop, a solar observatory, Earth observation and hundreds of experiments. Skylab's orbit eventually decayed and it disintegrated in the atmosphere on July 11, 1979, scattering debris across the Indian Ocean and Western Australia.
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In computing, a system call is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services, creation and execution of new processes, and communication with integral kernel services such as process scheduling. System calls provide an essential interface between a process and the operating system.
The Apollo Guidance Computer (AGC) was a digital computer produced for the Apollo program that was installed on board each Apollo command module (CM) and Apollo Lunar Module (LM). The AGC provided computation and electronic interfaces for guidance, navigation, and control of the spacecraft. The AGC was the first computer based on silicon integrated circuits. The computer's performance was comparable to the first generation of home computers from the late 1970s, such as the Apple II, TRS-80, and Commodore PET.
HAL/S is a real-time aerospace programming language compiler and cross-compiler for avionics applications used by NASA and associated agencies. It has been used in many U.S. space projects since 1973 and its most significant use was in the Space Shuttle program. It was designed by Intermetrics in 1972 for NASA and delivered in 1973. HAL/S is written in XPL, a dialect of PL/I. Although HAL/S is designed primarily for programming on-board computers, it is general enough to meet nearly all the needs in the production, verification, and support of aerospace and other real-time applications. According to documentation from 2005, it was being maintained by the HAL/S project of United Space Alliance.
VM is a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers.
CP/CMS is a discontinued time-sharing operating system of the late 1960s and early 1970s. It is known for its excellent performance and advanced features. Among its three versions, CP-40/CMS was an important 'one-off' research system that established the CP/CMS virtual machine architecture. It was followed by CP-67/CMS, a reimplementation of CP-40/CMS for the IBM System/360-67, and the primary focus of this article. Finally, CP-370/CMS was a reimplementation of CP-67/CMS for the System/370. While it was never released as such, it became the foundation of IBM's VM/370 operating system, announced in 1972.
Robert Laurel Crippen is an American retired naval officer and aviator, test pilot, aerospace engineer, and retired astronaut. He traveled into space four times: as pilot of STS-1 in April 1981, the first Space Shuttle mission; and as commander of STS-7 in June 1983, STS-41-C in April 1984, and STS-41-G in October 1984. He was also a part of the Manned Orbiting Laboratory (MOL), Skylab Medical Experiment Altitude Test (SMEAT), ASTP support crew member, and the Approach and Landing Tests (ALT) for the Space Shuttle.
Wen Tsing Chow, was a Chinese-born American missile guidance scientist and a digital computer pioneer, known for the invention of programmable read-only memory or PROM.
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CP-40 was a research precursor to CP-67, which in turn was part of IBM's then-revolutionary CP[-67]/CMS – a virtual machine/virtual memory time-sharing operating system for the IBM System/360 Model 67, and the parent of IBM's VM family. CP-40 ran multiple instances of client operating systems – particularly CMS, the Cambridge Monitor System, built as part of the same effort. Like CP-67, CP-40 and the first version of CMS were developed by IBM's Cambridge Scientific Center (CSC) staff, working closely with MIT researchers at Project MAC and Lincoln Laboratory. CP-40/CMS production use began in January 1967. CP-40 ran on a unique, specially modified IBM System/360 Model 40.
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This article covers the History of CP/CMS — the historical context in which the IBM time-sharing virtual machine operating system was built.
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