Technical Approaches
Cray frequently cited two important aspects to his design philosophy: remove heat, and ensure that all signals that are supposed to arrive somewhere at the same time do indeed arrive at the same time.
His computers were equipped with built-in cooling systems, extending ultimately to coolant channels cast into the mainframes and thermally coupled to metal plates within the circuit boards, and to systems immersed in coolants. In a story he told about himself, he realized early in his career that he should interlock the computers with the cooling systems so that the computers would not operate unless the cooling systems were operational. It did not originally occur to him to interlock in the other direction until a customer reported that localized power outages had shut down their computer, but left the cooling system running — so they arrived in the morning to find the machine encased in ice!
Cray addressed the problem of skew by ensuring that every signal path in his later computers was the same electrical length, so that values that were to be acted upon at a particular time were indeed all valid values. When required, he would run the traces back and forth on the circuit boards until the desired length was achieved, and he even employed Maxwell's equations in design of the boards to ensure that any radio frequency effects which altered the signal velocity and hence the electrical path length were accounted for.
When asked what kind of CAD tools he used for the Cray-1, Cray said that he liked #3 pencils with quad paper pads. Cray recommended using the backs of the pages so that the lines were not so dominant. When he was told that Apple Computer had just bought a Cray to help design the next Apple Macintosh, Cray commented that he had just bought a Macintosh to design the next Cray.
Read more about this topic: Seymour Cray
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