UNIVAC 1101 | 1950

 

The ERA 1101, later renamed the UNIVAC 1101, was designed and produced by Engineering Research Associates (ERA) in the early 1950s, and continued to be sold after Remington Rand acquired ERA. The initial military model of this computer system, the ERA Atlas, was the first stored-program computer successfully installed far from its manufacturing site. Remington Rand developed a series of machines based on the architecture of the 1101 until the 1960s.

ERA was formed by a group of codebreakers who worked for the U.S. Navy during World War II. This team produced several codebreaking machines similar to Britain’s famous Colossus computer, but designed for Japanese codes. After the war, the Navy wanted to keep the team intact, but they had to be officially discharged from naval service. As a result, ERA was established in a former Chase Aircraft shadow factory in St. Paul, Minnesota.

After the war, the team continued to produce codebreaking machines tailored to specific codes. However, when one of those codes changed and rendered their expensive computers useless, the team persuaded the Navy that creating a fully programmable computer was the only way to maintain a useful system. The Navy agreed, and in 1947 funded the development of the new system under the name "Project 13."

The resulting machine, known as the "Atlas," featured drum memory as its main memory and a simple central processing unit for integer operations. The first Atlas machine was installed at the Army Security Agency in December 1950. A faster version using William tubes and drums was delivered to the NSA in 1953.

The company began work on commercially selling the system. The Atlas was named after a character from the popular comic strip Barnaby, and they initially decided to name the commercial version "Mabel." However, Jack Hill suggested the name "1101," which is the binary representation of 13. The ERA 1101 was publicly announced in December 1951. A slightly modified version, the Atlas II, became the ERA 1103, while a more significantly modified version with core memory and floating-point math support was named UNIVAC 1103A.

During this period, the company became embroiled in lengthy and complex political machinations in Washington, D.C. Drew Pearson's "Washington Merry-Go-Round" claimed that the founding of ERA represented a conflict of interest for Norris and Engstrom, suggesting they used their wartime government connections to establish the company for their benefit. The resulting legal disputes had a substantial financial and emotional impact on the company. In 1952, due to these issues, it was acquired by Remington Rand.

Remington Rand had recently acquired the Eckert-Mauchly Computer Company, which produced the famous UNIVAC I, America’s first commercial computer. While ERA and UNIVAC operated separately within the company, the name "UNIVAC 1101" was chosen for the machine to leverage the well-known UNIVAC brand. Subsequently, a series of machines based on the same basic design was released and continued to be sold until the 1960s, when they were replaced by the similarly named UNIVAC 1100 series.

This computer measured 38 feet (12 meters) in length, 20 feet (6.1 meters) in width, and weighed about 8.4 short tons (7.6 tons), using 2,700 vacuum tubes for its logic circuits. The drum memory, with a diameter of 8.5 inches (22 centimeters), spun at 3,500 RPM and had 200 read-write heads. This memory could store 16,384 24-bit words (approximately 48 kB of memory), with access times ranging from 32 microseconds to 17 milliseconds.

Instructions were 24 bits long, with 6 bits for the operation code (opcode), 4 bits for the "skip" value (the number of memory locations to skip in the program order to move to the next instruction), and 14 bits for the memory address. Numbers were represented in binary, with negative numbers shown in one's complement form. Addition took 96 microseconds, and multiplication took 352 microseconds.

A single 48-bit accumulator essentially functioned as a subtraction mechanism, where addition was performed by subtracting the one's complement of the number to be added. While this may seem peculiar, the subtraction addition mechanism reduces the likelihood of negative zero occurring during normal operations.

This machine had a total of 38 instructions.