How to build your own 1:10 scale Cray-1 supercomputer

The Cray-1, released in 1976, was one of the most successful supercomputers of all time. The Freon-cooled computer was clocked at a heady 80MHz and capable of up to 250 megaflops -- much more than any other computer on the market at the time -- and best of all it looked like something out of Star Trek. Now, an enterprising hardware hacker has made his own Cray-1 supercomputer -- or at least, a 1:10 scale model of it -- using some wood, paint, and a Xilinx FPGA development board. Yes, after 38 years, an entire supercomputer can be boiled down to a single FPGA. Viva la Moore's law!

The original Cray-1 was a hulking beast that, including its Freon refrigeration system, weighed in at around 5.5 tons. For that, you got 1,662 printed circuit boards, each with up to 144 integrated circuits (chips) soldered on. The 64-bit (word-length) machine could address up to 1 megaword of main memory, and with the help of 12 pipelined execution units and a clock speed of 80MHz it could process up to 250 million floating point operations per second (megaflops).

Chris Fenton's 1:10 scale Cray-1(Opens in a new window) is... well... diminutive. There's no Freon, and there's no plate metal construction -- instead, there's just a Xilinx Spartan-3E 1600 development board that's programmed to closely match the Cray-1 architecture, and some hand-written software that roughly approximates the original Cray-1 operating system. The chassis is built out of MDF, balsa, pine, glue, and paint.

Bonus fun fact: The original Cray-1 was circular because the circuit boards had to be in exactly the right place to make sure communications between each module took exactly the right amount of time -- i.e. if the copper wires were slightly longer or shorter, the whole thing wouldn't work.

Why does Fenton's scale model only approximate the Cray-1's OS, I hear you ask? Well, much to the chagrin of zealous hardware hackers everywhere, it seems no one has a copy of the Cray-1 software. Just so you have some idea of how dedicated Fenton is, he even put in some Freedom of Information requests to various governmental agencies hoping they'd have some original disks (back then, supercomputers were mostly the reserve of national laboratories doing nuclear research). The Computer History Museum doesn't have a copy, either.

Fenton says he's tracked down a guy with an 80MB "disk pack" from the Cray-1 Maintenance Control Unit -- a dedicated computer that was used to boot the Cray-1, a bit like an original car/plane starter motor -- but hasn't yet seen what's on the disks.

So, for now, Fenton is stuck with a block diagram of the original Cray-1 architecture (pictured above), and writing software directly in machine code. It seems Fenton has only managed to get the FPGA up to 50MHz so far, too -- just shy of the original supercomputer's 80MHz. This is more related to the fact that Fenton's Spartan-3E only cost about $100 -- if he'd opted for a more expensive FPGA, 80MHz would've been easy to hit.

But best of all -- well, if you're an equally fervent DIY nut -- Fenton has released all of the source files that you'd need to build your own 1:10 Cray-1 model! There's the Verilog files for programming your FPGA, and a Python version of the Cray Assembly Language (CAL) compiler, so that you can write your own software.