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IBM 7090 console

The IBM 7090 is a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computers that was designed for "large-scale scientific and technological applications". The 7090 is 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 $2.9 million (equivalent to $18 million in 2017) or could be rented for $63,500 a month (equivalent to $405,000 in 2016).

The 7090 uses a 36-bit word length, with an address space of 32,768 words (15-bit addresses). It operates with a basic memory cycle of 2.18 μs, using the IBM 7302 Core Storage core memory technology from the IBM 7030 (Stretch) project.

With a processing speed of around 100 Kflop/s,[1] the 7090 is six times faster than the 709, and could be rented for half the price.[2]


Development and namingEdit

Although the 709 was a superior machine to its predecessor, the 704, it was being built and sold at the time that transistor circuitry was supplanting vacuum tube circuits. Hence, IBM redeployed its 709 engineering group to the design of a transistorized successor. That project became called the 709-T (for Transistorized), which because of the sound when spoken, quickly shifted to the nomenclature 7090 (i.e., seven - oh - ninety). Similarly, the related machines such as the 7070 and other 7000 series equipment were called by names of digit - digit - decade (e.g., seven - oh - seventy).[citation needed]

IBM 7094Edit

IBM 7094 operator's console showing additional index register displays in a distinctive extra box on top. Note "Multiple Tag Mode" light in the top center.

An upgraded version, the IBM 7094, was first installed in September 1962. It has seven index registers, instead of three on the earlier machines. The 7094 console has a distinctive box on top that displays lights for the four new index registers. photos The 7094 introduced double-precision floating point and additional instructions, but is largely backward compatible with the 7090. Minor changes in instruction formats, particularly the way the additional index registers are addressed, sometimes cause problems. On the earlier models, when more than one bit is set in the tag field, the contents of the two or three selected index registers are ORed, not added together, before the decrement takes place. On the 7094, if the three-bit tag field is not zero, it selects just one of seven index registers, however the "or" behavior remains available in a "multiple tag" compatibility mode.[3]

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, dual memory banks and improved overlap of instruction execution, an early instance of pipelined design.[4]

IBM 7040/7044Edit

In 1963, IBM introduced two new, lower cost machines called the IBM 7040 and 7044. They have a 36-bit architecture based on the 7090, but with some instructions omitted or optional, and simplified input/output that allows the use of more modern, higher performance peripherals from the IBM 1400 series. A 7094/7044 Direct Coupled System (DCS) was introduced later, with the 7094 performing computation while the 7044 handled Input/Output (I/O).

Transistors and circuitryEdit

The 7090 uses germanium alloy-junction transistors and (faster) germanium diffused junction[5] drift transistors. More than 50,000 in all.[6]

The 7090 uses the Standard Modular System (SMS) cards using current-mode logic[7] some using diffused junction drift transistors.[5]

Instruction and data formatsEdit

The basic instruction format is the same as the IBM 709, a three-bit prefix, 15-bit decrement, three-bit tag, and 15-bit address. The prefix field specifies the class of instruction. The decrement field often contains an immediate operand to modify the results of the operation, or is used to further define the instruction type. The three bits of the tag specify three index registers (seven in the 7094), the contents of which are subtracted from the address to produce an effective address. The address field contains either an address or an immediate operand.

  • Fixed-point numbers are stored in binary sign/magnitude format.
  • Single-precision floating-point numbers have a magnitude sign, an eight-bit excess-128 exponent and a 27-bit magnitude (the float number is binary rather than hexadecimal introduced later for system 360)
  • Double-precision floating-point numbers, introduced on the 7094, have a magnitude sign, an eight-bit excess-128 exponent, and a 54-bit magnitude. The double-precision number is stored in memory in an even-odd pair of consecutive words; the sign and exponent in the second word are ignored when the number is used as an operand.
  • Alphanumeric characters are six-bit BCD, packed six to a word.

Octal notation is used in documentation and programming; console displays lights and switches are grouped into three-bit fields for easy conversion to and from octal.


IBM 7090 operator's console at the NASA Ames Research Center in 1961, with two banks of IBM 729 magnetic tape drives. The card reader is in front of the man and woman at right.

The 7090 series features a data channel architecture for input and output, a forerunner of modern direct memory access I/O. Up to eight data channels can be attached, with up to ten IBM 729 tape drives attached to each channel. The data channels have their own very limited set of operations called commands. These are used with tape (and later, disk) storage as well as card units and printers, and offered high performance for the time. Printing and punched card I/O, however, employed the same modified unit record equipment introduced with the 704 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 using its fast 1400-series peripherals.


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 is 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 applicationsEdit

Dual 7090s at NASA during Project Mercury.

See alsoEdit


  1. ^ Performance of future high-end computers by David Bailey Lawrence Berkeley National Laboratory report
  2. ^ Pugh, Emerson W.; Johnson, Lyle R.; Palmer, John H. (1991). IBM's 360 and early 370 systems. MIT Press. p. 36. ISBN 0-262-16123-0. 
  3. ^ IBM 7094 Principles of Operation, p. 8
  4. ^
  5. ^ a b SMS DBZV: Two-Way AND, Type B
  6. ^ 7090 Data Processing System
  7. ^ SMS AA: Two-Way AND (current mode)
  8. ^ The IBM 7094 and CTSS Also contains links to many original CTSS documents
  9. ^ Riley, Christopher; Campbell, Dallas (23 October 2012). "The maths that made Voyager possible". BBC News. 
  10. ^ Shanks, D.; Wrench, Jr., J. W. (1962). "Calculation of π to 100,000 decimals". Mathematics of Computation. American Mathematical Society. 16 (77): 76–99. doi:10.2307/2003813. JSTOR 2003813. .
  11. ^ Roger N. Shepard (December 1964). "Circularity in Judgements of Relative Pitch" (PDF). Journal of the Acoustical Society of America. 36 (12): 2346–53. doi:10.1121/1.1919362. 
  12. ^ Morton, Peter (1989). Fire Across the Desert: Woomera and the Anglo-Australian Joint Project 1946-1980. Canberra: Australian Government Publishing Service. ISBN 0644475005. 
  • Reference Manual, IBM 7090 Data Processing System, 1961, IBM A22-6528-3

External linksEdit

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