UNIVAC I

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UNIVAC I at Franklin Life Insurance Company

The UNIVAC I (UNIVersal Automatic Computer I) was the first commercial computer made in the United States. It was designed principally by J. Presper Eckert and John Mauchly, the inventors of the ENIAC. Design work was begun by their company, Eckert-Mauchly Computer Corporation, and was completed after the company had been acquired by Remington Rand. (In the years before successor models of the UNIVAC I appeared, the machine was simply known as "the UNIVAC".)

The first UNIVAC was delivered to the United States Census Bureau on March 31, 1951 and was dedicated on June 14th that year.^[1] The fifth machine (built for the U.S. Atomic Energy Commission) was used by CBS to predict the result of the 1952 presidential election. With a sample of just 1% of the voting population it correctly predicted that Eisenhower would win. The UNIVAC I computers were built by Remington Rand's UNIVAC-division (successor of the Eckert-Mauchly Computer Corporation, bought by Rand in 1950).

[edit] History

[edit] Market positioning

As well as being the first American commercial computer, the UNIVAC I was the first American computer designed at the outset for business and administrative use (i.e. for the fast execution of large numbers of relatively simple arithmetic and data transport operations, as opposed to the complex numerical calculations required by scientific computers). As such the UNIVAC competed directly against punch-card machines (mainly made by IBM), but oddly enough the UNIVAC originally had no means of either reading or punching cards (which initially hindered sales to some companies with large quantities of data on cards, due to potential manual conversion costs). This was corrected by adding offline card processing equipment, the UNIVAC Card to Tape converter and the UNIVAC Tape to Card converter, to transfer data between cards and UNIVAC magnetic tapes.

[edit] Installations

Remington Rand employees, Harold E. Sweeney (left) and J. Presper Eckert (center) demonstrate the U.S. Census Bureau's UNIVAC for CBS reporter Walter Cronkite (right).

The first contracts were with government institutions such as the Census Bureau, the US Air Force, and the US Army Map Service. Contracts were also signed by the ACNielsen Company, and the Prudential Insurance Company. Following the sale of Eckert-Mauchly Computer Corporation to Remington Rand, due to the cost overruns on the project, Remington Rand convinced Nielsen and Prudential to cancel their contracts.

The first sale, to the Census Bureau, was marked with a formal ceremony on March 31, 1951 at the Eckert–Mauchly Division's factory at 3747 Ridge Avenue, Philadelphia. The machine was not actually shipped until the following December, because, as the sole fully set-up model, it was needed for demonstration purposes, and the company was apprehensive about the difficulties of dismantling, transporting, and reassembling the delicate machine.^[2] So the first installation was with the second computer, delivered to the Pentagon in June 1952.

UNIVAC installations, 1951–1954^[3]

Originally priced at US$159,000, the UNIVAC I rose in price until they were between $1,250,000 and $1,500,000. A total of 46 systems were eventually built and delivered.

The UNIVAC I was too expensive for most universities, and Sperry Rand, unlike companies such as IBM, was not strong enough financially to afford to give many away. However Sperry Rand donated UNIVAC I systems to Harvard University (1956), the University of Pennsylvania (1957), and Case Institute of Technology in Cleveland, Ohio (1957).

A few UNIVAC I systems stayed in service long after they were obsoleted by advancing technology. The Census Bureau used its two systems until 1963, amounting to twelve and nine years of service. Sperry Rand itself used two systems in Buffalo, New York until 1968. The insurance company Life and Casualty of Tennessee used its system until 1970, totaling over thirteen years of service.

[edit] Technical description

Model of UNIVAC I system, c. 1954 (courtesy of the Smithsonian). Central Complex shown to the upper left.

[edit] Major physical features

UNIVAC I used 5,200 vacuum tubes,^[4] weighed 29,000 pounds (13 metric tons), consumed 125 kW, and could perform about 1,905 operations per second running on a 2.25 MHz clock. The Central Complex alone (i.e. the processor and memory unit) was 4.3 m by 2.4 m by 2.6 m high. The complete system occupied more than 35.5 m² of floor space.

[edit] Main memory details

The main memory consisted of 1000 words of 12 characters. When representing numbers, they were written as 11 decimal digits plus sign. The 1000 words of memory consisted of 100 channels of 10 word mercury delay line registers. The input/output buffers were 60 words each, consisting of 12 channels of 10 word mercury delay line registers. There are 6 channels of 10 word mercury delay line registers as spares. With modified circuitry, 7 more channels control the temperature of the 7 mercury tanks, and one more channel is used for the 10 word "Y" register. The total of 126 mercury channels is contained in the 7 mercury tanks mounted on the backs of sections MT, MV, MX, NT, NV, NX, and GV. Each mercury tank is divided into 18 mercury channels.

Each 10 word mercury delay line channel is made up of three sections:

1. A channel in a column of mercury, with receiving and transmitting quartz piezo-electric crystals mounted at opposite ends.
2. An intermediate frequency chassis, connected to the receiving crystal, containing amplifiers, detector, and compensating delay, mounted on the shell of the mercury tank.
3. A recirculation chassis, containing cathode follower, pulse former and retimer, modulator, which drives the transmitting crystal, and input, clear, and memory-switch gates, mounted in the sections adjacent to the mercury tanks.

[edit] Instructions and data

Instructions were 6 alphanumeric characters, packed 2 per word. The addition time was 525 microseconds and the multiplication time was 2150 microseconds. A non-standard modification called "Overdrive" did exist, that allowed for three 4-character instructions per word under some circumstances. (Ingerman's simulator for the UNIVAC, referenced below, also makes this modification available.)

Digits were represented internally using excess-3 ("XS3") binary coded decimal (BCD) arithmetic with 6 bits per digit using the same value as the digits of the alphanumeric character set (and one parity bit per digit for error checking), allowing 11 digit signed magnitude numbers. But with the exception of one or two machine instructions, UNIVAC was considered by programmers to be a decimal machine, not a binary machine, and the binary representation of the characters was irrelevant. If a non-digit character was encountered in a position during an arithmetic operation the machine passed it unchanged to the output, and any carry into the non-digit was lost. (Note, however, that a peculiarity of UNIVAC I's addition/subtraction circuitry was that the "ignore", space, and minus characters were occasionally treated as numeric, with values of -3, -2, and -1 respectively, and the apostrophe, ampersand, and left parenthesis were occasionally treated as numeric, with values 10, 11, and 12.)

[edit] Input/output

Besides the operator's console, the only I/O devices connected to the UNIVAC I were up to 10 UNISERVO tape drives, a Remington Standard electric typewriter^{[citation needed]} and a Tektronix oscilloscope. The UNISERVO was the first computer tape drive and normally operated at 128 characters per inch on magnetically plated phosphor bronze tapes. The UNISERVO could also read and write UNITYPER created tapes at 20 characters per inch. The UNITYPER was an offline typewriter to tape device, used by programmers and for minor data editing. Backward and forward tape read and write operations were possible on the UNIVAC and were fully overlapped with instruction execution, permitting high system throughput in typical sort/merge data processing applications. Large volumes of data could be inputted via magnetic tapes created on offline card to tape system and outputted via a separate offline tape to printer system. The operators console had three columns of decimal coded switches that allowed any of the 1000 memory locations to be displayed on the oscilloscope. Since the mercury delay line memory stored bits in a serial format, a programmer or operator could monitor any memory location continuously and with sufficient patience, decode its contents as displayed on the scope. The on-line typewriter was typically used for announcing program breakpoints, checkpoints, and for memory dumps.

[edit] See also

• List of UNIVAC products
• History of computing hardware

[edit] Notes

1. ^ Reference: CNN's feature on the 50th anniversary of the UNIVAC.
2. ^ Lecture session, UNISYS Corporation, May 17–18, 1990, Smithsonian Institution,
3. ^ Ceruzzi, Paul E. A history of modern computing, MIT, 1998. The source notes that the list is compiled from a number of sources and does not include UNIVACs that were completed not delivered in the period 1951-54. In some cases the dates are approximate. Depending on the definition of "installed" the order may be slightly different.
4. ^ The vacuum tubes used in the UNIVAC I were mostly of type 25L6, but the machine also used tubes of type 6AK5, 7AK7, 6AU6, 6BE6, 6SN7, 6X5, 28D7, 807, 829B, 2050, 5545, 5651, 5687, 6AL5, 6AN5, 6AH6, 5V4, 5R4, 4D32, 3C23, and 8008.

[edit] External links

• UNIVAC Conference Oral history on 17-18 May 1990. Charles Babbage Institute, University of Minnesota, Minneapolis
• UNIVAC I documentation – From computer documentation repository www.bitsavers.org
• Unisys History Newsletter, Volume 5, Number 1 – From Randy Carpenter's home page at Georgia Tech
• The UNIVAC and the Legacy of the ENIAC – From the University of Pennsylvania Library (PENN UNIVERSITY/exhibitions)
• UNIVAC 1 Computer System – By Allan G. Reiter, formerly of the ERA division of Remington Rand
• UNIVAC Simulator 1.2 – By Peter Zilahy Ingerman; Shareware simulator of the UNIVAC I and II
• Core memory slide show – This slide show contains a photo of a 1951 core memory module for a UNIVAC I
• Remington-Rand Presents UNIVAC – Promotional film from the collection of the Computer History Museum, Mountain View, California