AN/USQ-17

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.[1] 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).[2]

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 main memory was 32,768 = 32K words of core memory.

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.