IBM 7090

IBM 7090

The IBM 7090 was a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computers and was designed for "large-scale scientific and technological applications". The 7090 was the third member of the IBM 700/7000 series scientific computers. The first 7090 installation was in November 1959. In 1960, a typical system sold for $2,900,000 or could be rented for $63,500 a month.

The 7090 used a 36-bit word length, with an address-space of 32K (32,768) words. It operated with a basic memory cycle of 2.18 μs, using the IBM 7302 Core Storage core memory technology from the IBM 7030 (Stretch) project.

IBM 7094 and IBM 7040/7044

An upgraded version, the IBM 7094, was first installed in September 1962. It had seven index registers, instead of three on the earlier machines. The 7094 console had a distinctive box on top that displayed lights for the four new index registers. photos The 7094 introduced double-precision floating point and additional instructions, but was largely backward compatible with the 7090. Minor changes in instruction formats, particularly the way the additional index registers were addressed, sometimes caused problems.

In 1963, IBM introduced lower cost machines with a similar architecture, but fewer instructions and simplified I/O, called the IBM 7040 and 7044. In April 1964, the first 7094 II was installed, which had almost twice as much general speed as the 7090 due to a faster clock cycle and introduction of overlapped instruction execution.

Instruction and data formats

The basic instruction format was a 3-bit prefix, 15-bit decrement, 3-bit tag, and 15-bit address. The prefix field specified the class of instruction. The decrement field often contained an immediate operand to modify the results of the operation, or was used to further define the instruction type. The three bits of the tag specified three index registers (seven in the 7094), the contents of which were subtracted from the address to produce an effective address. The address field contained either an address or an immediate operand.

  • Fixed point numbers were stored in binary sign/magnitude format.
  • Single precision floating point numbers had a magnitude sign, an 8-bit excess-128 exponent and a 27 bit magnitude
  • Double precision floating point numbers, introduced on the 7094, had a magnitude sign, an 8-bit excess-128 exponent, and a 54 bit magnitude. The double precision number was stored in memory in an even-odd pair of consecutive words; the sign and exponent in the 2nd word were ignored when the number was used as an operand.
  • Alphanumeric characters were 6-bit BCD, packed six to a word.

Octal notation was used in documentation and programming.


The 7090 series featured a data channel architecture for input and output, a forerunner of modern direct memory access I/O. Up to 8 data channels could be attached, with up to 10 IBM 729 tape drives attached to each channel. The data channels had their own, very limited, set of operations called commands. These were used with tape (and later, disk) storage as well as card units and printers, and offered high performance for the time. Printing and punch card I/O, however, employed modified unit record equipment and was slow. It became common to use a less expensive IBM 1401 computer to read cards onto magnetic tape for transfer to the 7090/94. Output would be spooled onto tape and transferred to the 1401 for printing or card punching using its much faster peripherals, notably the IBM 1403 line printer. Later IBM introduced the 7094/7044 Direct Coupled System, using data channel to data channel communication, with the 7094 primarily performing computations and the 7044 performing I/O operations.


The 7090 and 7094 machines were quite successful for their time, and had a wide variety of software provided for them by IBM. In addition, there was a very active user community within the user organization, SHARE.

IBSYS was a "heavy duty" production operating system with numerous subsystem and language support options, among them FORTRAN, COBOL, SORT/MERGE, the MAP assembler, and others.

FMS, the FORTRAN Monitor System, was a more lightweight but still very effective system optimized for batch FORTRAN and assembler programming. The assembler provided, FAP, (FORTRAN Assembly Program), was somewhat less complete than MAP, but provided excellent capabilities for the era. FMS also incorporated a considerably enhanced derivative of the FORTRAN compiler originally written for the 704 by Backus and his team.

Notable applications

  • The Compatible Time-Sharing System (CTSS), one of the first time-sharing operating systems, was developed at MIT's Project MAC using a 7094 with an extra bank of memory, among other modifications.
  • NASA used 7090s, and, later, 7094s to control the Mercury and Gemini space flights. During the early Apollo Program, a 7094 was kept operational to run flight planning software that had not yet been ported to mission control's newer System/360 computers.
  • The US Air Force retired its last 7094s in service from the Ballistic Missile Early Warning System ("BMEWS") in the 1980s after almost 30 years of use.
  • The US Navy continued to use a 7094 at Pacific Missile Test Center, Point Mugu, California through much of the 1980s, although a "retirement" ceremony was held in July 1982. Not all of the applications had been ported to its successor, a dual-processor CDC Cyber 175.
  • A pair of 7090s in Briarcliff Manor, NY, were the basis for the original version of the SABRE airlines reservation system introduced by American Airlines in 1962.
  • In 1961 Alexander Hurwitz used a 7090 to discover two Mersenne primes, with 1281 and 1332 digits - the largest prime numbers known at the time.
  • In 1961, the 7094 became the first computer to sing, singing the song Daisy Bell. Vocals were programmed by John Kelly and Carol Lockbaum and the accompaniment was programmed by Max Mathews. This performance was the inspiration for a similar scene in 2001: A Space Odyssey.
  • A 7090/1401 installation is featured in the motion picture Dr. Strangelove, with the 1403 printer playing a pivotal role in the plot (it is the hiding place for a transistor radio; which, when found and turned on by one of the three characters played by Peter Sellers in the film, reveals that the nuclear attack ordered by the deranged Air Force base commander is phony, and must be stopped at all costs).
  • The composer Iannis Xenakis wrote his piece "Atrées" using a IBM 7090 at Place Vendôme, Paris

See also


  • Reference Manual, IBM 7090 Data Processing System, 1961, IBM A22-6528-3

External links

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