From Academic Kids


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UNIVAC I central complex, containing the central processor and mercury memory.

The UNIVAC I (UNIVersal Automatic Computer I) was the first commercial computer made in the United States. It was designed by J. Presper Eckert and John Mauchly, the men behind the first American electronic computer, the ENIAC. During 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] (http://www.cnn.com/2001/TECH/industry/06/14/computing.anniversary/) The fifth (built for the Atomic Energy Commission) was used by CBS to predict the 1952 presidential election. With a sample of just 1% of the voting population it predicted that Eisenhower would win; something nobody would believe, but UNIVAC was right!

The UNIVAC I computers were built by Remington Rand's UNIVAC-division (successor of the Eckert-Mauchly Computer Corporation (EMCC), bought by Rand in 1950).


UNIVAC I used 5,200 vacuum tubes (mostly type 25L6 and 829B tubes), 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 mercury delay line memory unit alone was 14 feet by 8 feet by 8.5 feet high (4.3 m × 2.4 m × 2.6 m). The complete system occupied more than 350 ft² (35.5 m²) of floor space.

The main memory consisted of 1000 words of 11 decimal digits plus sign (72 bit words), consisting of 100 channels of 10 word mercury registers. The input and output memory is 120 words, consisting of 12 channels of 10 word mercury registers. There are 6 channels of 10 word mercury 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 channel is made up of three sections:

  1. A channel in a column of mercury, with receiving and transmitting quartz 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.

Instructions were 36 bits long, packed 2 per word. The addtion time was 525 microseconds and the multiplication time was 2150 microseconds.

Numbers were represented using excess-3 binary coded decimal (BCD) arithmetic with 6 bits per digit (and one parity bit per digit for error checking), allowing 11 digit signed magnitude numbers.


As well as being the first American commercial computer, the UNIVAC I was the first 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.

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Two Remington Rand employees demonstrate the UNIVAC for Walter Cronkite at the U.S. Census Bureau

The first contracts were with government institutions such as the Census Bureau, the US Air Force, and the 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. Following the first three UNIVAC I systems, two were sold to the Atomic Energy Commission, and one to the US Navy. The seventh UNIVAC I was installed at the Remington Rand sales office in New York City.

The eighth UNIVAC I, the first sale for business applications, was installed at the General Electric Appliance Division, to do payroll, in January 1954. DuPont bought the twelfth UNIVAC I, it was delivered in September 1954. Pacific Mutual Insurance received a UNIVAC I system in August 1955. Other insurance companies soon followed. As for government use, the Census Bureau got a second UNIVAC I in October 1954.

Originally priced at $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 for quite a long time—actually, long after they were obsolete by the evolving computing state of the art. 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.

External links

  • Manual of Operation for UNIVAC System (http://www.bitsavers.org/pdf/univac/univac1/UNIVAC1_OperMan.pdf) (PDF) – From computer documentation repository www.bitsavers.org
  • Unisys History Newsletter, Volume 5, Number 1 (http://www.cc.gatech.edu/gvu/people/randy.carpenter/folklore/v5n1.html) – From Randy Carpenter's home page at Georgia Tech
  • The UNIVAC and the Legacy of the ENIAC (http://www.library.upenn.edu/special/gallery/mauchly/jwm11.html) – From the University of Pennsylvania Library (PENN UNIVERSITY/exhibitions)
  • UNIVAC 1 Computer System (http://mywebpage.netscape.com/reitery2k/univac1.htm) – By Allan G. Reiter, formerly of the ERA division of Remington Rand
  • UNIVAC Simulator 1.2 (http://www.simtel.net/product.php?url_fb_product_page=57390) – By Peter Zilahy Ingerman; Shareware simulator of the UNIVAC I and II

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