TheAN/USQ-20, orCP-642[1][2][3] orNaval Tactical Data System (NTDS), was designed as a more reliable replacement for the Seymour Cray-designedAN/USQ-17 with the sameinstruction set. The first batch of 17 computers were delivered to the Navy starting in early 1961.[4]
A version of the AN/USQ-20 for use by the other military services andNASA was designated theUNIVAC 1206. Another version, designated theG-40, replaced the vacuum tubeUNIVAC 1104 in theBOMARC Missile Program.
The machine was the size and shape of an old-fashioned double-doorrefrigerator, about six feet tall (roughly 1.80 meters).
Instructions were represented as 30-bitwords 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-bitalphanumeric characters per word.
The main memory was 32,768 words ofcore memory.
The availableprocessor registers were:
