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The AN/USQ-17 or Naval Tactical Data System (NTDS) computer referred to in Sperry Rand documents as the Univac M-460, was Seymour Cray's last design for UNIVAC. UNIVAC later released a commercial version, the UNIVAC 490 and that system was later upgraded to a multiprocessor configuration as the 494.
The machine was the size and shape of a refrigerator, about four feet high (roughly 1.20 meters), with a hinged lid for access. However, shortly after completing the prototype design Cray left to join Control Data Corporation. When the Navy awarded Sperry Rand a US$50 million contract to build the AN/USQ-17, Univac engineers redesigned the entire machine from scratch using silicon transistors (retaining the instruction set so that programs developed for the original machine would still run on the new one).
As part of the redesign it was decided to improve access, and the second version was designed to stand upright, like an old fashioned double-door refrigerator, about six feet tall (roughly 1.80 m). This new design was designated the AN/USQ-20.
Instructions were represented as 30-bit words, in the following format:
f 6 bits function code j 3 bits jump condition designator k 3 bits partial word designator b 3 bits which index register to use y 15 bits operand address in memory
Numbers were represented as 30-bit words, this allowed for five 6-bit alphanumeric characters per word.
The available processor registers were:
- One 30-bit accumulator (A).
- One 30-bit Q register (combined with A to give a total of 60 bits for the result of multiplication or the dividend in division).
- Seven 15-bit index registers (B1–B7).
The instruction format defined for the AN/USQ-17 marked the beginning of an instruction set which would be carried on, with many changes along the way, into later UNIVAC computers including the UNIVAC 1100/2200 series which is still in use today[update].
- Marshall William McMurran (11 December 2008). ACHIEVING ACCURACY: A Legacy of Computers and Missiles. Xlibris Corporation. pp. 142–. ISBN 978-1-4628-1065-9.
- James A. Treadway (July 2005). Hard Charger!: The Story of the USS Biddle (DLG-34). iUniverse. pp. 107–. ISBN 978-0-595-36009-3.
- David L. Boslaugh (16 April 2003). When Computers Went to Sea: The Digitization of the United States Navy. John Wiley & Sons. pp. 165–. ISBN 978-0-471-47220-9.
- The Univac M-460 Computer – Paper by J. E. Thornton, M. Macaulay, and D. H. Toth, Remington Rand Univac Division of Sperry Rand (on-line version from Ed Thelen's Antique Computer Home Page)