CDC 8600

The introduction of integrated circuits solved the problems with dense packaging and liquid cooling addressed the heat issues.

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.

[1] 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 (3') across and high, sitting on top of a ring of power supplies.

This technique, today known as SIMD, reduced the total number of memory accesses because the instruction was only read once, instead of four times.

[1] In 1971, Control Data was undergoing a "belt tightening" due to the cost of an ongoing lawsuit against IBM, and asked all divisions to reduce their payroll by 10%.

In this case Cray decided the current design was a dead-end, and told William Norris (CDC's CEO) that the only way forward was to redesign the machine from scratch.

The finances of the company were dangerous, and Norris decided that he could not take the risk; Cray would have to continue with the current design.

For his new work he abandoned the multiprocessor concept, concerned that software of the era would be unable to take full advantage of the CPUs.

He may have come to this conclusion after the ILLIAC IV finally entered operation at about the same time, and proved to have disappointing performance.

Jim Thornton's competing STAR design had reached production quality at this point, and the 8600 project was then cancelled.