The AN/USQ-17 or Navy Tactical Data System (NTDS) computer referred to in Sperry Rand documents as the Univac M-460, was Seymour Cray's last design for Univac.
The machine was the size and shape of a bathtub, about four feet high, with a hinged lid for access.
However, shortly after completing the design Cray left to join Control Data Corporation. So when the Navy awarded Sperry Rand a $50 million contract to build the AN/USQ-17, the loss of the engineers that understood the machine forced Sperry to redesign the entire machine from scratch (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. 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 memoryNumbers were represented as 30-bit words, this allowed for five 6-bit alphanumeric characters per word.
The available 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 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.