CDC 7600 and 8600
In the same month it won its lawsuit against IBM, CDC also announced its new computer, the CDC 7600 (previously referred to as the 6800 within CDC). This machine's hardware clock speed was almost four times that of the 6600 (36 MHz vs. 10 MHz) a 27.5 ns clock cycle, and it offered considerably more than four times the total throughput.
Much of this speed increase was due to extensive use of pipelining, a technique that allows different parts of the CPU to work simultaneously on different parts of successive instructions of the process at the same time. This works in the same way that an automotive assembly line can produce one vehicle every 90 seconds, and thus easily 300 vehicles per 8 hour shift by doing a partial assembly of each vehicle simultaneously every 90 seconds. Any one vehicle will still take several hours to be completely assembled. In computers, pipelining uses separate circuits to work on different parts of different instructions at the same time, in a fashion similar to the many stations on an assembly line. Any one instruction completes processing no faster, but the program as a whole moves through the computer more quickly.
The 7600 did not do well in the marketplace because it was introduced in the 1969 downturn in the U.S. national economy. Its complexity had led to poor reliability. The machine was slightly incompatible with the 6000-series, so it required a completely different operating system, which like most new OSs, was primitive. The 7600 project paid for itself, yet it damaged CDC's reputation. The 7600 memory had a split primary- and secondary-memory which required user management but was more than fast enough to make it the fastest uniprocessor 1969 to 1976. A few dozen 7600s were the supercomputer of choice at supercomputer centers around the US and world.
Cray then turned to the design of the CDC 8600. This design included four 7600-like processors in a single, smaller case. The smaller size and shorter signal paths allowed the 8600 to run at much higher clock speeds, and in combination with higher speed memory, these features provided most of the performance gains. The 8600, however, belonged to the "old school" in terms of its physical construction, and it used individual components soldered to circuit boards. The design was so compact that cooling and servicing the CPU modules proved effectively impossible. An abundance of hot-running solder joints ensured that the machines did not work reliably; Cray recognized that a re-design was needed.
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