The search for the lost Cray supercomputer OS

In 1976, famed computer architect Seymour Cray released one of the most successful supercomputers ever made: the Cray-1, a stylish 5.5-ton C-shaped tower that was quickly embraced by laboratories all over the world. While it soon gave way to newer, faster Cray models that then faded away entirely in the ’90s due to huge cost and performance advances in supercomputing, its iconic shape and early success left a lasting legacy in the industry.

Seymour Cray and a Cray-1 supercomputer. Photo courtesy of Cray.

Seymour Cray and a Cray-1 supercomputer. Photo courtesy of Cray.

That legacy led hobbyists Chris Fenton and Andras Tantos to pose what they thought would be a simple question to answer: How can I build a Cray-1 for my desk?

A tiny replica takes shape

In 2010, Fenton, a New York City-based electrical engineer who actually works on modern supercomputers, decided to replicate the physical form of the computer. Its hardware was well-documented online, so building it came together quickly. Fenton used a CNC machine and glue to build the tower and bench out of wood. Then he painted the tower and covered the bench in pleather. The complete model is 1/10 the size of the original Cray.

Chris Fenton scale model of Cray-1
Chris Fenton scale model of Cray-1

Considering that an iPad packs far more computing power than a Cray-1, it wasn’t difficult to find a board option that could handle emulating the original Cray computational architecture. Fenton settled on the $225 Spartan 3E-1600, which is tiny enough to fit in a drawer built into the bench. Considering the first Crays cost between $5 and 8 million, that’s a pretty impressive bargain.

A lead emerges from a Minnesota basement

But while Fenton was able to replicate the architecture, he hit a wall when he began searching for software to make the Cray model fully operational. He determined none of the code from the original OS was available via the internet, so he went analog. He asked the Computer History Museum and government whether they had a copy laying around. Nope.

His first lead came via a friend who introduced him to Donald Lee, a former Cray software engineer who had “this giant 10-pound disk pack” — an early, removable medium for data storage — in the basement of his Minnesota home. Lee told me last week that he isn’t exactly sure how the disk ended up in his possession, but he might have picked it up at a garage sale or when someone was cleaning house before leaving Cray.

Cray-1 disk pack

To run the disk, Fenton needed a disk drive. He borrowed a 1970s-era one from the Museum of Information Technology at Arlington in Texas. Poor archival conditions had left the drive in rough shape, so he cobbled together a system involving a robot made from the innards of a MakerBot Thing-O-Matic. The robot slowly passed over the disk, allowing a converter to change the data from analog to digital and feed it onto Fenton’s computer.

The disk drive. Photo courtesy of Chris Fenton

The disk drive. Photo courtesy of Chris Fenton

Disappointingly, the disk pack only held factory-testing software.

A second disk pack surfaces

The publicity Fenton garnered via his documentation of the project caught the attention of Andy Gelme, an Australian software developer who once worked for Cray. He too had a disk pack.

Concerned that shipping would damage or demagnetize the disk, a friend of Gelme’s couriered it to Fenton during a planned trip to New York City a few weeks later. While the disk didn’t contain the original Cray-1 OS, it did carry the last ever version of the Cray OS, which was made for a Cray-1 successor: the Cray X-MP.

Fenton used the recovery system he developed with the disk drive to pull information off the disk. He was not able to convert it into working software, but he had begun to correspond with Tantos, a Microsoft electrical engineer, who had independently been pursuing the Cray OS.

Tantos took over working with the disk. He rewrote the recovery tools, plus a simulator for the software and supporting equipment like printers, monitors, keyboards and more. For the greater part of the last year, he arduously reverse engineered the OS from the image. Despite a few remaining bugs, the Cray OS now works.


Fenton is now in the process of upgrading his desktop machine to be compatible with the Cray X-MP OS. The two are also on the lookout for a compiler: a computer program that would allow them to write their own applications and feed them into the Cray.

“For these machines (Cray-1 or X-MP) you couldn’t really go into a store and buy an application, like you do for a PC these days. Now, you just ‘install’ Word and it runs. For these machines, everything came in source-code format and you needed to compile it before you could run it. You use the … compiler to turn it into machine code the machine could understand,” Tantos said. “That was the main way you interacted with these machines. Without the compiler, you can’t feed it that.”

If you have any information that could help Fenton and Tantos, you can contact them here.

Preserving what’s available

Both hobbyists say they tackled the project for fun, but found it to be an important exercise in the preservation of computing history. Despite the fame of these early computers, little effort was made to ensure full documentation survived.


“In some ways it’s sad, but in other ways it’s fascinating,” Tantos said. “Seeing how extremely hard it is to come by software for these early computers, it’s even more important that we preserve what is available.

When they finally are able to pair the OS with Fenton’s desk model, it will be both novel and historical, as it will be the first working “Cray” in decades.

“The Cray-1 is one of those iconic machines that just makes you say ‘Now that’s a supercomputer!’” Fenton wrote on his blog in 2010. “Sure, your iPhone is 10X faster, and it’s completely useless to own one, but admit it … you really want one, don’t you?