The IBM System/360 Model 91 was announced in 1964 as a competitor to the

CDC 6600 The CDC 6600 was the flagship of the 6000 series of mainframe computer systems manufactured by Control Data Corporation. Generally considered to be the first successful supercomputer, it outperformed the industry's prior recordholder, the I ...

. Functionally, the Model 91 ran like any other large-scale

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 applicati ...

, but the internal organization was the most advanced of the System/360 line, and it was the first IBM computer to support out-of-order instruction execution. It ran

OS/360 OS/360, officially known as IBM System/360 Operating System, is a discontinued batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was influenced by the earlier IBSYS/IBJOB a ...

as its operating system. It was designed to handle high-speed data processing for scientific applications. This included

space exploration Space exploration is the process of utilizing astronomy and space technology to investigate outer space. While the exploration of space is currently carried out mainly by astronomers with telescopes, its physical exploration is conducted bo ...

theoretical astronomy Theoretical astronomy is the use of analytical and computational models based on principles from physics and chemistry to describe and explain astronomical objects and astronomical phenomena. Theorists in astronomy endeavor to create theoretical ...

, sub-atomic physics and global weather forecasting. The first Model 91 was used at the

NASA Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C., in Greenbelt, Maryland, United States. Established on May 1, 1959, as NASA's first space flight center, GSFC ...

in 1968 and at the time was the most powerful computer in user operation. It was capable of executing up to 16.6 million instructions per second, making it roughly equivalent to an Intel 80486SX-20 MHz CPU or AMD 80386DX-40 MHz CPU in MIPS performance. The CPU consisted of five autonomous units: instruction, floating-point, fixed-point, and two storage controllers for the overlapping memory units and the I/O data channels. The

floating-point unit A floating-point unit (FPU), numeric processing unit (NPU), colloquially math coprocessor, is a part of a computer system specially designed to carry out operations on floating-point numbers. Typical operations are addition, subtraction, multip ...

made heavy use of

instruction pipelining In computer engineering, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming in ...

and was the first implementation of Tomasulo's algorithm. It was also one of the first computers to utilize multi-channel memory architecture. Castells-Rufas et al. reported that the 360/91 used 74kW of power.

Models

There were four models of the IBM System/360 Model 91. They differed by their main memory configuration, all using IBM's 2395 Processor Storage. The 91K had 2 MB, using one 2395 Model 1. Both the 91KK and the 91L came with 4 MB of main memory: the former used a pair of 2395 Model 1s, the latter a single 2395 Model 2. The 6 MB KL was equipped with one Model 1 and one Model 2 IBM 2395s.

Models built

There were only 15 Model 91s ever produced, four of which were for IBM's internal use. After quoting from Pugh et al, William H. Blair says "Many disagree on the number of 360/91s that IBM built or sold. I have read and heard it authoritatively stated that the number was 10, 11, 12, 14, 15, or 20." As for those delivered to customers, "a 360/85 was delivered from when a 91 was ordered until it was ready."

Differences from standard System/360 behaviour

Because of the emphasis on speed, there were some minor differences in the system's behaviour: # Floating point divide results could differ in the least significant bit. # Some exceptions were imprecise. # The handling of floating point underflow and overflow was different, although arguably better. # Memory stores could occur out of sequence. A memory barrier instruction was added to allow control of this where necessary.

IBM and NASA

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

had a long history with

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

including the use of IBM components on crewed space flights such as the IBM ASC-15 on Saturn 1, the IBM ASC-15B on the Titan Family, IBM GDC on Gemini, IBM LVDC on Saturn 1B/5, IBM System/4 Pi-EP on the MOL, and the IBM System/4 Pi-TC 1 on the

Apollo Telescope Mount The Apollo Telescope Mount, or ATM, was a crewed Sun, solar observatory that was a part of Skylab, the first American space station. It could observe the Sun in wavelengths ranging from soft X-rays, ultraviolet, and visible light. The ATM was ...

and

Skylab 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. Skylab was constructe ...

. The Model 91 was shipped 9 months late to the

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C., in Greenbelt, Maryland, United States. Established on May 1, 1959, as NASA's first space flight center, GSFC ...

in October 1967 and did not begin regular operations until January 1968 after it passed the federal government operations testing.

IBM System/360 Model 95

The Model 95 was a variant of the Model 91 with 1 megabyte of thin-film memory and 4 megabytes of core memory. NASA acquired the only two 360/95s ever built. The console of the Model 95, for which no Functional Characteristics manuals exist, was identical to that of the 360/91.

First internet connected server

In 1971,

UCLA The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California, United States. Its academic roots were established in 1881 as a normal school then known as the southern branch of the C ...

used an IBM 360/91 to provide "production computing services" to

ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first computer networks to implement the TCP/IP protocol suite. Both technologies became the tec ...

. The services it provided included job submittal, a "mailbox" system and

FTP The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and dat ...

In popular culture

There is a Model 91 Panel that is currently on display at the Living Computer Museum in

Seattle, Washington Seattle ( ) is the List of municipalities in Washington, most populous city in the U.S. state of Washington (state), Washington and in the Pacific Northwest region of North America. With a population of 780,995 in 2024, it is the List of Unit ...

that was borrowed and featured in the movie ''Tomorrowland'' (2015).

References

External links

IBM System/360 Model 91 Functional Characteristics

{{DEFAULTSORT:IBM System 360 Model 91 Computing platforms System/360 Model 91