CDC 8600

The CDC 8600 was the last of Seymour Cray's supercomputer designs while working for the Control Data Corporation. As the natural successor to the CDC 6600 and CDC 7600, the 8600 was intended to be about 10 times as fast as the 7600, already the fastest computer on the market.

Development started in 1968, shortly after the release of the 7600, but the project soon started to bog down. By 1971 CDC was having cash-flow problems and the design was still not coming together, prompting Cray to leave the company in 1972. The 8600 design effort was eventually cancelled in 1974, and Control Data moved on to the CDC STAR-100 series instead.

In the 1960s computer design was based on mounting electronic components (transistors, resistors, etc.) on circuit boards. Several boards would be used to make a discrete logic element of the machine, known as a module. Overall machine cycle speed is strongly related to the signal path – the length of the wiring – requiring high-speed computers to make their modules as small as possible. This was at odds with the need to make the modules themselves more complex in order to increase functionality. By the late 1960s the individual components had stopped getting much smaller, so in order to increase the complexity of the machines, the modules would have to grow. In theory, this could slow the machine down due to signalling delays.

Cray aimed to solve these contradictory problems by doing both; making each module larger and crammed with many more components, while at the same time making the computer as a whole smaller by packing the modules closer together inside the machine. Between the time the 7600 was developed and work on the 8600 began, there had been no process improvements in the components themselves, so any performance improvements had to come solely from packaging. For the new design, they used modules containing eight four-layer circuit boards about 8" by 6", resulting in a stack the size of a large textbook and using up about 3 kilowatts of power. The modules were then packed into a mainframe chassis that was comparatively tiny, a 16-sided cylinder about one meter across and high, sitting on top of a ring of power supplies. Perhaps unsurprisingly, the 8600 bears a strong resemblance to the later Cray-1.

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