America’s First Computer


Today in Military History: On Aug. 7, 1944, IBM handed over its Automatic Sequence Controlled Calculator (ASCC) to Harvard University where is it known as the Harvard Mark 1. Fifty-one feet long, eight feet high, two feet deep and weighing nearly 10,000 pounds, it was America’s first automatic digital calculator and the largest electromechanical calculator ever.

Envisioned by Harvard’s Howard Aiken in the 1930s, IBM started work on the “Automated Computing Plant” in 1939. Costing some $200,000, it had seven major parts composed of 760,000 components that, according to IBM, “consisted of an interlocking panel of small gears, counters, switches and control circuits, all only a few inches in depth. The ASCC used 500 miles (800 km) of wire with 3 million connections, 3,500 multipole relays with 35,000 contacts, 2,225 counters, 1,464 tenpole switches and tiers of 72 adding machines, each with 23 significant numbers.” Key to its operation was a 50-foot shaft powered by a five horsepower motor.

“The Mark I was a parallel synchronous calculator that could perform table lookup and the four fundamental arithmetic operations, in any specified sequence, on numbers up to 23 decimal digits in length. It had 60 switch registers for constants, 72 storage counters for intermediate results, a central multiplying-dividing unit, functional counters for computing transcendental functions, and three interpolators for reading functions punched into perforated tape,” according to IBM. “Numerical input was in the form of punched cards, paper tape or manually set switches. The output was printed by electric typewriters or punched into cards. Sequencing of operations was accomplished by a perforated tape.”

Each second, it could do three addition or subtraction calculations. Full capacity multiplication took 5.7 seconds, while division took 15.3 seconds. Logarithmic and trigonometric function functions each took more than 60 seconds.

Instructions were read from a 24-channel punched paper tape – divided into three fields of eight channels – and executed one after another. Another tape contained input numbers, but without the ability deviate from its planned sequence, complex calculations were lengthy. By joining the ends of the tape, a closed program loop was created.

Manhattan Project scientist John von Neumann used the Mark I in March to calculate if implosion would detonate an atom bomb and the machine did work in May for the US Navy Bureau of Ships.

The computer was used for 15 years and retired in 1959.

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