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The IBM 701

A Complete History Of Mainframe Computing
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The IBM 701


While most of our esteemed readers have a good idea of IBM's dominance in the world of computing from the mid to late 20th century, what may be less-known is where it starts, how and why it happened, and how it progressed. Let's start with one of the two computers it developed at the same time as the UNIVAC.

We'll begin with the IBM 701, which was a direct competitor to the esteemed UNIVAC. Announced in 1952, there were many similarities between the 701 and the UNIVAC, but many differences as well. Memory was not stored in a mercury-delay line, but in 3" vacuum tubes referred to as "William's Tubes," in deference to their inventor. Although they were more reliable than normal vacuum tubes, they still proved to be the greatest source of unreliability for the computer. However, one benefit was that all bits of a word could be retrieved at once, as opposed to the UNIVAC's mercury delay lines, where memory was read bit by bit. The CPU was also considerably faster than the UNIVAC's, which could almost perform 2,200 multiplications per second, compared to 455 for the UNIVAC. It could also execute almost 17,000 additions and subtractions, as well as most other instructions, per second. This was remarkable for that time. IBM's eight million byte tape drive was also very good and could stop and start much faster than the UNIVAC's and was capable of reading or writing 12,500 digits per second. However, unlike the UNIVAC with its elegant buffers, the processor had to handle all I/O operations, which could severely impact performance on heavily I/O-based applications.

In 1956, IBM introduced a technology known as RAMAC, which was the first magnetic disk system for computers. It allowed data to be quickly read from anywhere on the disk and could be attached not just to the 701, but to IBM's other computers, including the 650, which we will look at next. As most of you no doubt realize, this technology is the progenitor to the hard disks that are very much with us today.

IBM produced 19 701 units, which were fewer than the number of UNIVACs made, but still enough to prevent Remington Rand from dominating the field. The cost was a serious inhibitor to more widespread use, setting the user back over $16,000 a month. Also, as mentioned, the 701 was only part of IBM's response. The 650 was the other.

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