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The EDVAC as installed in Building 328 at the Ballistics Research Laboratory.

EDVAC (Electronic Discrete Variable Automatic Computer) was one of the earliest electronic computers. Unlike its predecessor the ENIAC, it was binary rather than decimal, and was a stored program computer.

Project and plan[edit]

ENIAC inventors John Mauchly and J. Presper Eckert proposed the EDVAC's construction in August 1944, and design work for the EDVAC commenced before the ENIAC was fully operational. The design would implement a number of important architectural and logical improvements conceived during the ENIAC's construction and would incorporate a high-speed serial-access memory.[1] Like the ENIAC, the EDVAC was built for the U.S. Army's Ballistics Research Laboratory at the Aberdeen Proving Ground by the University of Pennsylvania's Moore School of Electrical Engineering. Eckert and Mauchly and the other ENIAC designers were joined by John von Neumann in a consulting role; von Neumann summarized and discussed logical design developments in the 1945 First Draft of a Report on the EDVAC.[2]

A contract to build the new computer was signed in April 1946 with an initial budget of US$100,000. The contract named the device the Electronic Discrete Variable Automatic Calculator. The final cost of EDVAC, however, was similar to the ENIAC's, at just under $500,000.

Technical description[edit]

The EDVAC was a binary serial computer with automatic addition, subtraction, multiplication, programmed division and automatic checking with an ultrasonic serial memory[1] capacity of 1,000 44-bit words (later set to 1,024 words, thus giving a memory, in modern terms, of 5.5 kilobytes).

Physically, the computer comprised the following components:

  • a magnetic tape reader-recorder (Wilkes 1956:36[1] describes this as a wire recorder.)
  • a control unit with an oscilloscope
  • a dispatcher unit to receive instructions from the control and memory and direct them to other units
  • a computational unit to perform arithmetic operations on a pair of numbers at a time and send the result to memory after checking on a duplicate unit
  • a timer
  • a dual memory unit consisting of two sets of 64 mercury acoustic delay lines of eight words capacity on each line
  • three temporary tanks each holding a single word[1]

EDVAC's average addition time was 864 microseconds (about 1,160 operations per second) and its average multiplication time was 2.900 microseconds (about 340 operations per second). Time for an operation depended on memory access time, which varied depending on the memory address and the current point in the serial memory's recirculation cycle.

The computer had almost 6,000 vacuum tubes and 12,000 diodes, and consumed 56 kW of power. It covered 490 ft² (45.5 m²) of floor space and weighed 17,300 lb (7,850 kg). The full complement of operating personnel was thirty people per eight-hour shift.

Installation and operation[edit]

EDVAC was delivered to the Ballistics Research Laboratory in August 1949. After a number of problems had been discovered and solved, the computer began operation in 1951 although only on a limited basis. Its completion was delayed because of a dispute over patent rights between Eckert and Mauchly and the University of Pennsylvania, resulting in Eckert and Mauchly's resignation and departure to form the Eckert–Mauchly Computer Corporation and taking most of the senior engineers with them.

By 1960 EDVAC was running over 20 hours a day with error-free run time averaging eight hours. EDVAC received a number of upgrades including punch-card I/O in 1953, extra memory in slower magnetic drum form in 1954, and a floating point arithmetic unit in 1958.

EDVAC ran until 1961 when it was replaced by BRLESC. During its operational life it proved to be reliable and productive for its time.

See also[edit]


  1. ^ a b c d Wilkes, M. V. (1956). Automatic Digital Computers. New York: John Wiley & Sons. pp. 305 pages. QA76.W5 1956. 
  2. ^ "First Draft of a Report on the EDVAC" (PDF format) by John von Neumann, Contract No.W-670-ORD-4926, between the United States Army Ordnance Department and the University of Pennsylvania. Moore School of Electrical Engineering, University of Pennsylvania, June 30, 1945. The report is also available in Stern, Nancy (1981). From ENIAC to UNIVAC: An Appraisal of the Eckert–Mauchly Computers. Digital Press. 

External links[edit]