or Navy Tactical Data System
(NTDS), was designed as a more reliable replacement for the 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
The machine was the size and shape of an old fashioned double-door refrigerator, about six feet tall.
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 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.