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. Harvard University is a private university in Cambridge, Massachusetts, USA, and a member of the Ivy League. ... Howard Hathaway Aiken is considered one of the pioneers of the computer field, being the primary engineer behind IBMs Harvard Mark I computer. ... The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ...

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.) A unique feature of the Mark II is that it had built-in hardware for several functions such as the reciprocal, square toot, logarithm, exponential, and some trigonometric functions. These took between five and twelve seconds to execute. Portion of the Harvard-IBM Mark 1, left side. ... A microsecond is an SI unit of time equal to one millionth (10-6) of a second. ...

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 was 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. The so-called von Neumann architecture is a model for a computing machine that uses a single storage structure to hold both the set of instructions on how to perform the computation and the data required or generated by the computation. ... An instruction set, or instruction set architecture (ISA), describes the aspects of a computer architecture visible to a programmer, including the native datatypes, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O (if any). ... The term Harvard architecture originally referred to computer architectures that used physically separate storage and signal pathways for their instructions and data (in contrast to the von Neumann architecture). ...

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. Dahlgren is a census-designated place located in King George County, Virginia. ...

References:

• A History of Computing Technology, Michael R. Williams, 1997, IEEE Computer Society Press, ISBN 0-8186-7739-2

Also see: Harvard Mark I, Howard Aiken. Portion of the Harvard-IBM Mark 1, left side. ... Howard Hathaway Aiken is considered one of the pioneers of the computer field, being the primary engineer behind IBMs Harvard Mark I computer. ...