There's an old story that “The people at Cray design their supercomputers with Apple systems, and the Apple designers use Crays!” Apart from this being a terrific example of recurring rotational serendipity (what goes around, comes around) is there any truth to it?
Like many urban legends, this one contains a nugget of truth. The 1991 Annual Report of Cray Research, Inc., contained a short article describing how Apple used a Cray for designing Macintosh cases. The Cray is used to simulate the injection molding of the plastic enclosure cases. The Mac II case was the first Apple system to benefit from the modeling, and the trial was successful. The simulation identified warping problems that were solved by prototyping, thus saving money in tooling and production. Apple also uses its Cray for simulating air flow inside the enclosure to check for hot spots. The Cray magazine also reported that the Apple PowerBook continues to use supercomputer simulations. (Cray Channels, Spring 1996, pp.10-12 “Apple Computer PowerBook computer molding simulation”).
The inverse story holds that Seymour Cray himself used a Macintosh to design Crays. The story seems to have originated with an off-the-cuff remark from Seymour Cray, who had a Macintosh at home and used it to store some of his work for the Cray 3. Common sense suggests that the simulation of discrete circuitry (Verilog runs, logic analysis, and so on), which is part of all modern integrated circuit design, is done far more cost-effectively on a large server farm than on a microprocessor. Cray probably has a lot of supercomputer hardware ready for testing as it comes off the production line.
It's conceivable that a Macintosh could be used to draft the layout of blinking lights for the front of a Cray, or choose some nice color combinations, or some other non-CPU intensive work. A Macintosh is a very good system for writing design notes, sending email, and drawing diagrams, all of which are equally essential parts of designing a computer system.
The good folks at Cray Research have confirmed in a Cray Users' Group newsletter that they have a few Macs on the premises.While it's unlikely that they run logic simulations on their Macs, we can indeed chalk it up as only-slightly-varnished truth that “the people at Cray design their supercomputers with Apple systems, and the Apple designers use Crays”.
All the action in supercomputers is in clusters these days, not in super-powerful monolithic mainframes. Also bear in mind that Moore's Law means that the desk-side G5 Mac in 2004 (236 MFLOP) is more powerful than the Cray 1 (160 MFLOP) super computer reigning nearly 30 years earlier in 1976.