UNIVAC 1103

UNIVAC 1103
Company type	Computer
Industry	Computer hardware
Predecessor	UNIVAC 1101
Founded	October 1953
Founder	Seymour Cray (designer)
Parent	Engineering Research Associates (design), Remington Rand (manufacturer)

The UNIVAC 1103, also known as the ERA 1103, was the follow-up to the UNIVAC 1101 and was created by Engineering Research Associates with manufacturing carried out by Remington Rand in October 1953. This model is notably recognized as the first computer designed by Seymour Cray.

History

Prior to finalizing the Atlas (UNIVAC 1101), the United States Navy tasked Engineering Research Associates with developing a more advanced system, referred to as Task 29 or Atlas II.

In 1952, ERA requested permission from the Armed Forces Security Agency, which later became the NSA, to commercialize Atlas II. This authorization mandated the elimination of classified instructions, leading to the creation of the commercial UNIVAC 1103. Because of security restrictions, Remington Rand's management was initially kept uninformed about this development. The first commercial unit was sold to aircraft producer Convair, where Marvin Stein operated it.

Remington Rand publicly introduced the UNIVAC 1103 in February 1953, positioning it within the scientific computing sector against rivals such as the IBM 701. By early 1954, a Joint Chiefs of Staff panel evaluated both machines for a Joint Numerical Weather Prediction initiative. The findings indicated comparable processing speeds, though IBM was preferred due to its superior input/output performance.

The subsequent model, the UNIVAC 1103A, also called Univac Scientific, improved dependability by substituting Williams tube memory with magnetic-core memory. It incorporated hardware floating-point commands and implemented an early version of hardware interrupt functionality. This line was later succeeded by the UNIVAC 1105.

Technical details

The system’s logic comprised roughly 3,900 vacuum tubes—primarily triodes—and about 9,000 diodes, featuring at least a dozen different types of tubes. Memory included electrostatic storage via 36 Williams tubes, each storing 1,024 bits, providing a total of 1,024 words with a word length of 36 bits. Additionally, a magnetic drum memory offered 16,384 words. Both memory types were directly addressable: electrostatic memory occupied addresses from 0 to 01777 (Octal), while drum memory covered addresses from 040000 to 077777 (Octal).

Numbers in fixed-point format used a single sign bit and 35 bits for value representation in ones' complement. Instructions consisted of a 6-bit operation code and two operand addresses of 15 bits each.

Programming environments included Remington-Rand’s RECO assembler; RAWOOP assembler and SNAP floating point interpreter from the Ramo-Wooldridge Corporation; FLIP floating point system developed by Consolidated Vultee Aircraft; and CHIP floating-point interpreter created at Wright-Patterson Air Force Base.

The approximate weight of the UNIVAC 1103/A was .

1103A

Launched in March 1956, the UNIVAC 1103A represented an enhanced iteration incorporating magnetic-core memory and additional processor interrupt capabilities. It accommodated up to 12,288 words of 36-bit magnetic-core memory distributed among one to three banks, each containing 4,096 words.

Fixed-point data utilized a single sign bit alongside a 35-bit value expressed in ones' complement format, whereas floating-point numbers consisted of a sign bit, an eight-bit exponent, and a 27-bit mantissa. The instruction set comprised a six-bit opcode paired with two operand addresses of 15 bits each.

The 1103A directly rivaled the IBM 704, sharing technological features such as vacuum-tube logic circuits, magnetic-core memory, and hardware designed for floating-point calculations.

One model was acquired by NACA's Lewis Research Center (which later became NASA), initially equipped with 1,096 words of 36-bit magnetic core memory and a magnetic drum storing 16,384 words. Operating at a clock frequency of 500 KHz, it utilized teletype-style punched tape for input/output operations. Over the next ten years, NASA extensively upgraded this system: replacing the original magnetic core with a commercial solid-state core memory of 16,384 words; adding an eight-unit magnetic tape storage system; incorporating a floating-point arithmetic unit; and implementing an indirect addressing unit. These solid-state components were integrated with the original vacuum tube electronics to improve both performance and reliability.

1104

The 1104 was a 30-bit adaptation of the 1103 developed in 1957 for Westinghouse Electric to support the BOMARC Missile Program. However, by the time BOMARC was deployed during the 1960s, the UNIVAC 1104 had been replaced by a more sophisticated computer system—the G-40—derived from the AN/USQ-20 series.

1105

Released by Sperry Rand in September 1958, the UNIVAC 1105 succeeded the UNIVAC 1103A model. Its principal improvements included a buffered input/output system and an optional third memory cabinet that expanded magnetic-core memory capacity by an additional 4,096 words.