IBM 360

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Watson announcing the 360 [1]

IBM System/360,
a 32-bit mainframe computer system family announced by IBM's 2nd president, Thomas Watson, Jr. on April 7, 1964, and delivered between 1965 and 1978. The chief architect of System/360 was Gene Amdahl, the project was managed by Fred Brooks.


Early 360 models used Solid Logic Technology. The 360/195 (1971) had ECL integrated circuits for the arithmetic and logic operations in the central processor combined with the 32 KiB high speed buffer memory. Each silicon memory chip was about 0.125 inches square and consisted of 664 transistors and diodes etc. Each memory chip stored 64 bits of data. Two memory chips were mounted on a 0.5 inch ceramic substrate [2]. A typical 360/195 configuration would be a single CPU with 2 MiB core memory, an operator's console with a cathode-ray tube (CRT) display for diagnostics and operator control [3].


The System/360 had a pipelined architecture with 16 32-bit general-purpose registers, four 64-bit floating-point registers, and 24-bit (16 MiB) byte-addressable interleaved memory of Big-endian byte/word order. Most models used microcode to implement the instruction set. Machine instructions had operators with operands, which could contain register numbers or memory addresses. Binary arithmetic and logical operations are performed as register-to-register and as memory-to-register/register-to-memory as a standard feature, and had 4-bit nibble , 8-bit byte, 16-bit halfword, 32-bit word , 64-bit double word or 128-bit quad word memory operands, or even 2048 byte storage blocks [4]. Five separate units allowed the 360/195 to overlap and process up to seven different operations at the same time. The floating-point unit could handle up to two additions and a multiplication at one time.



Mike Alexander at the console of the IBM S/360 Model 67 ca 1969 [5]


Installation of the IBM 360/91 at Columbia University in 1969
The machine ran J. Biit at ACM 1970, and CCCP at ACM 1971 [6] [7]


Master on the 360/195. Alex Bell, Geoff Lambert, Peter Kent, John Birmingham and John Waldron [8]

Chess Programs

See also

Selected Publications

External Links

IBM System/360

History of IBM - 1960–1968: The System/360 era
IBM System/360 architecture
IBM System/360 Model 67
IBM Archives: Mainframes introduction 2
IBM Archives: System/360 Model 91
Inside System/360 from The Computer History Museum


Operating Systems




  1. Watson announcing the IBM System/360 from The Computer History Museum, Courtesy of the IBM Corporate Archive, IBM claimed that the April 7, 1964 System/360 announcement was made to more than 100,000 people gathered in 165 cities
  2. System/360 Model 195 - Circuit Technology from Atlas Computer Laboratory
  3. System/360 Model 195 - Configuration from Atlas Computer Laboratory
  4. IBM System/360 architecture - Memory - Wikipedia
  5. Computing Center staff member Mike Alexander sitting at the console of the IBM S/360 Model 67 Duplex mainframe computer at the North University Building on the main campus of the University of Michigan in Ann Arbor, Michigan, sometime between 1968 and 1971, by Dave Mills, Michigan Terminal System from Wikipedia, source Michigan Terminal System
  6. Installation of the IBM 360/91 in the Columbia Computer Center machine room in February or March 1969. Photo: AIS archive, The IBM 360/91 - Columbia University
  7. IBM Archives: System/360 Model 91
  8. Slide 28: 23.08.74 to 01.11.74 from Rutherford's Photographic Section for the Atlas Computer Laboratory

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