IBM 7090

The IBM 7090 was a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computers and was designed for "large-scale scientific and technological applications". The 7090 was the third member of the IBM 700/7000 series scientific computers. The first 7090 installation was in November 1959. In 1960, a typical system sold for $2.9 million (equal to $54 million in 2016) or could be rented for $63,500 a month (equal to $1206,000 in 2016).

The 7090 used a 36-bit word length, with an address space of 32,768 words. It operated with a basic memory cycle of 2.18 μs, using the IBM 7302 Core Storage core memory technology from the IBM 7030 (Stretch) project.

With a processing speed of around 100 Kflop/s, the 7090 was six times faster than the 709, and could be rented for half the price.

Although the 709 was a superior machine to its predecessor, the 704, it was being built and sold at the time that transistor circuitry was supplanting vacuum tube circuits. Hence, IBM redeployed its 709 engineering group to the design of a transistorized successor. That project became called the 709-T (for Transistorized), which because of the sound when spoken, quickly shifted to the nomenclature 7090 (i.e., seven - oh - ninety). Similarly, the related machines such as the 7070 and other 7000 series equipment were called by names of digit - digit - decade (e.g., seven - oh - seventy).

An upgraded version, the IBM 7094, was first installed in September 1962. It had seven index registers, instead of three on the earlier machines. The 7094 console had a distinctive box on top that displayed lights for the four new index registers. photos The 7094 introduced double-precision floating point and additional instructions, but was largely backward compatible with the 7090. Minor changes in instruction formats, particularly the way the additional index registers were addressed, sometimes caused problems. On the earlier models, when more than one bit was set in the tag field, the contents of the two or three selected index registers were ORed, not added together, before the decrement took place. On the 7094, if the three-bit tag field was not zero, it selected just one of seven index registers, however the "or" behavior remained available in a "multiple tag" compatibility mode.

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