The AN/USQ-20, or CP-642 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. 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.

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: