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The IBM 704

A Complete History Of Mainframe Computing
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The IBM 704

Announced in 1954, the IBM 704 was the first large-scale commercially-available computer system to employ fully automatic floating-point arithmetic commands and the first to use the magnetic core memory developed for the Whirlwind.

Core memory consisted of tiny doughnut-shaped metal pieces that were roughly the size of a pin-head with wires running through them, which could be magnetized in either direction, giving a logical value of zero or one. Core memory had a lot of important advantages, not the least of which was that it did not need power to maintain its contents (an advantage it holds over modern memory). It also allowed truly random access, where any memory location was accessed as quickly as any other (except when interleaving was used, of course). This was not the case with prior forms of memory. It was considerably faster than other memory technologies used, having an access time of 12 microseconds. Perhaps most importantly, however, was the much greater reliability that the IBM 704 offered.

For longer-term storage, the 704 used a magnetic drum storage unit. For additional storage, tapes capable of holding five million characters each were used.

The 704 was quite fast, being able to perform 4,000 integer multiplications or divides per second. However, as mentioned, it was also capable of doing floating point arithmetic natively and could perform almost 12,000 floating-point additions or subtractions per second. More than this, the 704 added index registers, which not only dramatically sped up branches, but also reduced program development time (since this was handled in hardware now).

The 704 pioneered two major technologies we have today: the index registers and floating-point arithmetic. Magnetic core memory was also extremely useful, offering far greater speed and reliability, but it was a transient technology.

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