AN/USQ-20

The AN/USQ-20, or CP-642^[1][2][3] or Naval Tactical Data System (NTDS), was designed as a more reliable replacement for the Seymour Cray-designed AN/USQ-17 with the same instruction set. The first batch of 17 computers were delivered to the Navy starting in early 1961.^[4]

The AN/USQ-20 computer.

A version of the AN/USQ-20 for use by the other military services and NASA was designated the UNIVAC 1206. Another version, designated the G-40, replaced the vacuum tube UNIVAC 1104 in the BOMARC Missile Program.

In accordance with the Joint Electronics Type Designation System (JETDS), the "AN/USQ-20" designation represents the 20th design of an Army-Navy electronic device for general utility special combination equipment. The JETDS system also now is used to name all Department of Defense electronic systems.

Technical

The machine was the size and shape of an old-fashioned double-door refrigerator, about six feet tall (roughly 1.80 meters).

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 words of core memory.

The available processor registers were:

• One 30-bit arithmetic (A) register.
• A contiguous 30-bit Q register (total of 60 bits for the result of multiplication or the dividend in division).
• Seven 15-bit index (B) registers (note: register B0 is always zero).

See also

• Electronics portal

• List of military electronics of the United States
• CMS-2
• List of UNIVAC products
• History of computing hardware
• Military computers