EDVACEDVAC (Electronic Discrete Variable Automatic Computer) was one of the earliest electronic computers. It was binary rather than decimal and was the first with stored program space. It was based on ENIAC, but included certain improvements which time had prevented being included on ENIAC and was intended to be smaller and simpler. EDVAC was also built for the U.S. Army's Ballistics Research Laboratory by the University of Pennsylvania. The ENIAC designers Eckert and Mauchly were joined by John von Neumann and some others and the new design was based on von Neumann's 1945 report on ENIAC. A contract to build the new computer was signed in April 1946 with an initial budget of $100,000 and the contract named the device the Electronic Discrete Variable Automatic Calculator. The final cost of EDVAC was similar to ENIAC at just under $500,000. The computer that was built was to be binary with automatic addition, subtraction, multiplication, programmed division and automatic checking with a memory capacity of 1,000 words (later set to 1,024 words). Physically the computer was built out of the following components - a magnetic tape reader-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; and a dual memory unit consisting of two sets of 64 mercury acoustic delay lines of eight words capacity on each line and also three temporary tanks each holding a single word. A major concern in construction was to balance reliability and economy. Physically EDVAC had almost 6,000 vacuum tubes and 12,000 diodes, it consumed 56 KW of power. It covered 490 ft2 of floor and weighed 17,300 lbs. The typical operating personnel were thirty people for each eight-hour shifts. EDVAC was delivered to the Ballistics Research Laboratory in August 1949 and after a number of problems had been discovered and solved the computer began operation in 1951 although only on a limited basis. 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, it had proved to be highly reliable and productive.