Harvard Mark II

The Harvard Mark II was an electromechanical computer built at Harvard University under the direction of Howard Aiken and was finished in 1947. It was financed by the United States Navy.

Related Topics:
Harvard University - Howard Aiken - United States Navy

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Unlike the Harvard Mark I, the Mark II was built out of high-speed electromagnetic relays instead of mechanical counters. This is one reason that it was much faster than the Mark I. (The other reason was that it was funded by the US Navy, which could obtain state-of-the-art parts.) Its addition time was 125,000 microseconds and the multiplication time was 750,000 microseconds. (This was a factor of 2.6 and a factor 8 faster, respectively, compared to the Mark I.) It was the second machie (after the Bell Labs Relacy Calculator) to have floating-point hardware. A unique feature of the Mark II is that it had built-in hardware for several functions such as the reciprocal, square root, logarithm, exponential, and some trigonometric functions. These took between five and twelve seconds to execute.

Related Topics:
Harvard Mark I - Microseconds

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The Mark II was not a stored-program computer ? it read an instruction of the program one at the time from a tape and executed it (like the Mark I). This seperation of data and instructions is known as the Harvard architecture. The Mark II had a peculiar programming method that was devised to ensure that the contents of a register were available when needed. The tape containing the program could encode only eight instructions, so what a particular instruction code meant depended on when it was executed. Each second was divided up into several periods, and a coded instruction could mean different things in different periods. An addition could be started in any of eight periods in the second, a multiplication could be started in any of four periods of the second, and a transfer of data could be started in any of twelve periods of the second. Although this system worked, it made the programming complicated, and it reduced the efficiency of the machine somewhat.

Related Topics:
Stored-program computer - Instruction - Harvard architecture

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The Mark II ran some realistic test programs in July 1947. It was delivered to the US Navy Proving Ground at Dahlgren, Virginia in 1947 or 1948.

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