UNIVAC 1101

The UNIVAC 1101, or ERA 1101, was a computer system designed by Engineering Research Associates (ERA) and built by the Remington Rand corporation in the 1950s. It was the first stored program computer in the United States.

Originally designed for the US Navy's Bureau of Ships (an NSA cover) and called Atlas (after the character [1] Archived February 24, 2013 at the Wayback Machine. in the popular comic strip Barnaby). The commercial version was renamed 1101 because it was designed under "Task 13" (1101 is 13 in the binary system).

The computer measured 11.5 m long by 6 m wide and used 2,700 vacuum tubes for its logic circuits. Its drum memory measured 216 mm in diameter, rotated at 3,500 rpm, had 200 read-write heads, and could hold 16,384 24-bit words (a memory size equivalent to 48 kB).

The instructions occupied 24 bits, with 6 bits for the opcode, 4 bits for the "jump" (indicating how many memory locations to jump to get the next instruction in the program sequence), and 14 bits for the memory address. Numbers were represented in the binary system with negative values represented as one's complement. The addition time was 96 microseconds and the multiplication time was 352 microseconds.

The simple 48-bit accumulator was fundamentally subtractive, addition was carried out by subtracting one's complement from the number to be added. This may seem quite strange, but the subtractive adder reduces the probability of getting negative zero in normal operations.

History

Engineering Research Associates built two Atlas systems for the Navy's Bureau of Ships, installing them in December 1950 and March 1953. There was talk of calling the commercial version MABEL, but instead Of this, Jack Hill suggested 1101. The ERA 1101 was publicly announced in December 1951.

Engineering Research Associates built a third machine for its own offices with the intention of creating a service for other companies in need of computing resources. However, this failed and in November 1954 Remington Rand donated the machine to the Georgia Institute of Technology for a asking price of $500,000. In November 1958 Georgia Tech upgraded the machine with 4,096 words of magnetic core memory at a cost of $39,400. This 1101 was still running student jobs in 1961.