Harvard Mark II

See also: Mark II

The Harvard Mark II was an electromechanical computer builds with the Université of Harvard under the direction of Howard $aiken and was finished in 1947. It was financed by the marine of the the United States.

Mark II was built with electromagnetic relai S at high-speed rather than with electromechanical meters like those used for the Harvard Mark I, which makes it much faster than its predecessor. The time put for an addition was of 0,125 second and time for a multiplication was of 0,75 second. There is thus had an acceleration by factors of 2,6 and 8, respectively, in comparison with Mark I. It was the second machine (after the Bell Labs Relay Calculator) to have material with not floating. A single characteristic of Mark II is that it has several functions the such Réciproque, the square Racine, the Logarithme, the Exponentiel and certain functions trigonometrical S built in version material and not software. These functions took between 5 and 12 seconds to be carried out.

Mark II was not a computer with recorded program - it read a Instruction program at the same time starting from a band and to carry out it (as Mark I did it). This separation of the data and the instructions is known under the name of Architecture Harvard. Mark II had a method of particular programming which was conceived of kind to ensure that the contents of a register were available when he was asked. The band containing the program could encoder only eight instructions, and thus what a particular instruction code meant depended on the moment when it was carried out. Each second was divided into several periods, and an instruction could mean various things during different time. An addition could be started with any eight periods of the second, a multiplication could be started with any four periods of the second, and a transfer of information could begin with any the twelve periods from the second. Although this system functioned, it made the programming complicated, and it reduced in a certain way the effectiveness of the machine.

Mark II made turn certain realistic test programs in July 1947. It was delivered to the center of test of the US Navy Dahlgren (Virginia) in 1947 or 1948.

Data-processing first bug

The use of the " term; bug" (French bug) to describe unexplainable defects had been already current in the jargon of the engineers for several decades; the word could be used originally in design of electronic material or electromechanics to describe mechanical dysfunctions. For example, the term was used by Thomas Edison, and also during the Second world war for the electronic problems of the Radar S.

The first case documented of " Bug informatique" related to a moth (mite) wedged in relay 70 of the panel F of the " Mark II $aiken Relay Calculator" (another denomination of Harvard Mark II) whereas it was tested on September 9th, 1947. Grace Hopper stuck the mite in the Journal of laboratory under the title " First actual box off bug being found" (first effective case of " bug" with being found). The operators D-utilisérent then the word " bug" by saying that they had " débuggé" the machine, thus introducing the term of " debuggage" (debugging) in data processing.

See too

Harvard Mark I
Harvard Mark III
Harvard Mark IV

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