A Cray-Z Cool Supercomputer Watch

Compared to the computer you are using now they may not be very powerful, but during the earlier days of digital computing in the 1970s and 1980s, Cray supercomputers were a thing to behold. Their megabytes of memory and multiple processors running at hundreds of megahertz seemed almost too good to be true for those that were playing Bubble Bobble on a Commodore 64 or Tandy Color Computer. In addition to the computing power, Cray supercomputers also caught people’s eyes with their futuristic designs that made them look like they belonged in the engine room of the USS Enterprise.

For some of us, that fascination with Cray computers has endured through the years. An electrical engineer named Chris Fenton, who builds modern supercomputers by day, still enjoys playing with Cray technologies by night. Fenton has long been designing hardware simulations of various Cray supercomputers in FPGAs. But despite the relatively modest capabilities of these systems, FPGAs that can fit in all of the components have been on the expensive side.

Just recently Moore’s law finally smiled upon Fenton’s projects, however, and it is now possible to simulate a Cray C90 (reasonably closely, anyway), on an inexpensive and compact development board. Given that fact — and also that Fenton had a really cool circular display that was just begging to be included in a project (we all know how that goes!) — the only logical course of action was to build a scale model of a Cray C90 into a wristwatch.

The build is centered around a Diligent CMOD-A7 FPGA board. This runs a single Cray CPU core at 105 MHz. Not bad for a wristwatch, although the real deal had 16 CPUs running at 244 MHz. There is also a Teensy 3.6 microcontroller packed into the watch to serve as a front-end computing unit. The microcontroller drives the OLED display, issues reset signals to the simulated Cray, and also initializes the system memory. The distinctive C90 casing was 3D-printed.

While these development boards are quite small, they are not small by wristwatch standards. As such, this 1/25th scale Cray C90 looks a bit absurd on the wrist. But it is definitely not meant to be practical, as is evidenced by what is on the display. A standard time and date display, you think? Ha! No, this watch shows you a simulation of the motions of Jupiter and 63 of its moons, with each body interacting with every other body (and achieving a sustained 40 MFLOPS). To decode these positions and determine the actual time, you will need another Cray supercomputer!

You might get a good workout from wearing this watch on your wrist if you decide to make your own, but at some point you will most certainly tire of it catching and snagging on everything in sight due to its massive size. But the watch can just as easily sit on your desk as a novelty toy, which is what Fenton is using it for these days. Be sure to check out the full project write-up for more details and some interesting Cray history.