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The ERA 1101, later renamed UNIVAC 1101, was a computer system designed and built by Engineering Research Associates (ERA) in the early 1950s and continued to be sold by the Remington Rand corporation after that company later purchased ERA. Its (initial) military model, the ERA Atlas, was the first stored-program computer that was moved from its site of manufacture and successfully installed at a distant site. Remington Rand used the 1101's architecture as the basis for a series of machines into the 1960s.

The Univac 1101 belongs to the UNIVAC 1100/2200 series (called Univac Scientific Computers).[1][2]



ERA was formed from a group of code-breakers working for the United States Navy during World War II. The team had built a number of code-breaking machines, similar to the more famous Colossus computer in England, but designed to attack Japanese codes. After the war the Navy was interested in keeping the team together even though they had to formally be turned out of Navy service. The result was ERA, which formed in St. Paul, Minnesota in the hangars of a former Chase Aircraft shadow factory.

After the war, the team continued to build codebreaking machines, targeted at specific codes. After one of these codes changed, making an expensive computer obsolete, the team convinced the Navy that the only way to make a system that would remain useful was to build a fully programmable computer. The Navy agreed, and in 1947 they funded development of a new system under "Task 13".

The resulting machines, known as "Atlas", used drum memory for main memory and featured a simple central processing unit built for integer math. The first Atlas machine was built, moved, and installed at the Army Security Agency by December 1950.[3][self-published source][4][5] A faster version using Williams tubes and drums was delivered to the NSA in 1953.


The company turned to the task of selling the systems commercially. Atlas was named after a character in the popular comic strip Barnaby,[6] and they initially decided to name the commercial versions "Mabel". Jack Hill suggested "1101" instead; 1101 is the binary representation of the number 13. The ERA 1101 was publicly announced in December 1951.[7][5] Atlas II, slightly modified became the ERA 1103,[8] while a more heavily modified version with core memory and floating point math support became the UNIVAC 1103A.

At about this time the company became embroiled in a lengthy series of political maneuverings in Washington, DC. Drew Pearson's Washington Merry-Go-Round claimed that the founding of ERA was a conflict of interest for Norris and Engstrom because they had used their war-time government connections to set up a company for their own profit. The resulting legal fight left the company drained, both financially and emotionally. In 1952 they were purchased by Remington Rand, largely as a result of these problems.

Remington Rand had recently purchased Eckert–Mauchly Computer Corporation, builders of the famed UNIVAC I, the first commercial computer in the US. Although ERA and UNIVAC were run separately within the company, looking to cash in on the UNIVAC's well known name, they renamed the machine to become the "UNIVAC 1101". A series of machines based on the same basic design followed, and were sold into the 1960s before being replaced by the similar-in-name-only UNIVAC 1100 family.



This computer was 38 ft (12 m) long, 20 ft (6.1 m) wide, weighed about 8.4 short tons (7.6 t)[5][9][10] and used 2700 vacuum tubes for its logic circuits. Its drum memory was 8.5 in (22 cm) in diameter, rotated at 3500 rpm, had 200 read-write heads, and held 16,384 24-bit words (a memory size equivalent to 48 kB) with access time between 32 microseconds and 17 milliseconds.

Instructions were 24 bits long, with six bits for the opcode, four bits for the "skip" value (telling how many memory locations to skip to get to the next instruction in program sequence), and 14 bits for the memory address. Numbers were binary with negative values in ones' complement. The addition time was 96 microseconds and the multiplication time was 352 microseconds.

The single 48-bit accumulator was fundamentally subtractive, addition being carried out by subtracting the ones' complement of the number to be added. This may appear rather strange, but the subtractive adder reduces the chance of getting negative zero in normal operations.

The machine had 38 instructions.

Instruction set[edit]


y is memory box at address y X = X-Register (24 digits)
( ) is interpreted as the contents of Q = Q-Register (24 digits)
A = Accumulator (48 digits)
Insert (y) in A Insert complement of (y) in A
Insert (y) in A [multiple precision] Insert complement of (y) in A [multiple precision]
Insert absolute value (y) in A Insert complement of absolute value (y) in A
Add (y) to (A) Subtract (y) from (A)
Add (y) to (A) [multiple precision] Subtract (y) from (A) [multiple precision]
Add absolute value of (y) to (A) Subtract absolute value of (y) from (A)
Insert (Q) in A Clear right half of A
Add (Q) to (A) Transmit (A) to Q
Insert [(y) + 1] in A
Multiply and divide
Form product (Q) * (y) in A Add logical product (Q) * (y) to (A)
Form logical product (Q) * (y) in A Divide (A) by (y), (quotient forms in Q, non-negative remainder left in A)
Add product (Q) * (y) to (A)
Logical and control flow
Store right half of (A) at y Shift (A) left
Store (Q) at y Shift (Q) left
Replace (y) with (A) using (Q) as operator Take (y) as next order
Replace (y) with (A) [address portion only] Take (y) as next order if (A) is not zero
Insert (y) in Q Take (y) as next order if (A) is negative
Take (y) as next order if (Q) is negative
Input Output and control
Print right-hand 6 digits of (y) Optional Stop
Print and punch right-hand 6 digits of (y) Intermediate Stop
Final Stop

See also[edit]


  1. ^ Adams, Armand E.; Armstrong, Dorothy P.; Armstrong, Lancelot W.; Bartik, Jean; Carter, Lee S.; Chinitz, M. Paul; Danehower, George; Delves, Eugene L.; Dixon, Donald B.; Hammer, Carl; Holberton, Frances E.; Huff, Morgan W.; Koons, Florence K.; Marquardt, Donald W.; Matter, H. W.; Sammet, Jean E.; Sberro, Joseph E.; Shuler, Cecil M.; Swearingen, John K.; Tonik, Albert B.; Wilson, Louis D.; Woltman, Frances B.; Woltman, Richard D. (May 1990). Armstrong, Dorothy P. "UNIVAC conference". Charles Babbage Institute / Oral History Interviews: 54. hdl:11299/104288. [...] the 1100 series was called the Univac Scientific Computers.
  2. ^ "Hagley Museum and Library: Sperry Corporation, UNIVAC Division photographs and audiovisual materials (1985.261) -- Audiovisual Collections and Digital Initiatives Department". d. Univac scientific computers (St. Paul), 1953-1962. Retrieved 2018-05-22. The "Univac scientific computers" subseries contains images of the 1103, 1105 and 1107 "scientific computers," built by Univac Federal Systems Division, St. Paul.
  3. ^ McMurran, Marshall William (2008). ACHIEVING ACCURACY: A Legacy of Computers and Missiles. Xlibris Corporation. pp. 36–37. ISBN 9781462810659.
  4. ^ "1. The ERA 1101 Computer". Digital Computer Newsletter. 3 (1): 1, 2. April 1951.
  5. ^ a b c Boslaugh, David L. (2003). When Computers Went to Sea: The Digitization of the United States Navy. John Wiley & Sons. pp. 96–98. ISBN 9780471472209.
  6. ^ [1]
  7. ^ Pugh, Emerson W. (1995). Building IBM: Shaping an Industry and Its Technology. MIT Press. p. 142. ISBN 9780262161473.
  8. ^ Flamm, Kenneth (2010). Creating the Computer: Government, Industry and High Technology. Brookings Institution Press. ISBN 978-0815707219.
  9. ^ Weik, Martin H. (December 1955). "UNIVAC-SCI (ERA-1101)". ed-thelen.org. A Survey of Domestic Electronic Digital Computing Systems.
  10. ^ (16,000 lbs + 17,400 lbs ) / 2 = 16,700 pounds (8.4 short tons)
    16,000 pounds (8.0 short tons; 7.3 t)
    17,400 pounds (8.7 short tons; 7.9 t)
  11. ^ "Automatic Computing Machinery: Discussions - Minimum Access Programming". Mathematics of Computation. 6 (39): 172–182. 1952. doi:10.1090/S0025-5718-52-99392-7. ISSN 0025-5718.

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