Cray versus Raspberry Pi

My former boss (Steve Parker, RIP) shared a story of Turner Whitted making predictions about how much compute would be needed to achieve real-time ray tracing, some time around when his seminal paper was published (~1980). As the story goes, Turner went through some calculations and came to the conclusion that it’d take 1 Cray per pixel. Because of the space each Cray takes, they’d be too far apart and he thought they wouldn’t be able to link it to a monitor and get the results in real time, so instead you’d probably have to put the array of Crays in the desert, each one attached to an RGB light, and fly over it in an airplane to see the image.

Another comparison that is equally astonishing to the RPi is that modern GPUs have exceeded Whitted’s prediction. Turner’s paper used 640x480 images. At that resolution, extrapolating the 160 Mflops number, 1 Cray per pixel would be 49 Tera flops. A 4080 GPU has just shy of 50 Tflops peak performance, so it has surpassed what Turner thought we’d need.

Think about that - not just faster than a Cray for a lot less money, but one cheap consumer device is faster than 300,000 Crays.(!) Faster than a whole Cray per pixel. We really have come a long, long way.

The 5090 has over 300 Tflops of ray tracing perf, and the Tensor cores are now in the Petaflops range (with lower precision math), so we’re now exceeding the compute needed for 1 Cray per pixel at 1080p. 1 GPU faster than 2M Crays. Mind blowing.

Back in 2020, someone built a working model of a Cray-1.[1] Not only is it instruction compatible, using an FPGA, it's built into a 1/10 scale case that looks like a Cray-1.

The Cray-1 is really a very simple machine, with a small instruction set. It just has 64 of everything. It was built from discrete components, almost the last CPU built that way.

[1] https://www.cpushack.com/2010/09/15/homebrew-cray-1a-1976-vs...

In 2013 I'd just built a new top-spec PC. I looked up the performance and then back-calculated using the TOP500† and I believe it would have been the most powerful supercomputer in the world in about 1993. If you back-calculated further, I think around 1980 it became more powerful than every computer on the planet combined.

† https://en.wikipedia.org/wiki/TOP500

And you can 3D print a Cray YMP case for your Raspberry Pi: https://www.thingiverse.com/thing:6947303

The pi has a sub $100 accelerator card that takes it to 30 TFLOPs. So you can add three more orders of magnitude of performance for a rough doubling of the price.

Reading this I wonder, say we did have a time machine and were somehow able to give scientists back in the day access to an RPI5. What sort of crazy experiments would that have spawned?

I'm sure when the Cray 1 came out, access to it must have been very restricted and there must have been hoards of scientists clamoring to run their experiments and computations on it. What would have happened if we gave every one of those clamoring scientists an RPI5?

And yes I know this raises an interface problem of how would they even use one back in the day but lets put that to the side and assume we figured out how to make an RPI5 behave exactly like a Cray 1 and allowed scientists to use it in a productive way.

> but then again if you'd showed me an RPi5 back in 1977 I would have said "nah, impossible" so who knows?

I was reading lots of scifi in 1977, so I may have tried to talk to the pi like Scotty trying to talk to the mouse in Star Trek IV. And since you can run an LLM and text to speech on an RPi5, it might have answered.

It is a frequent fantasy of mine to bring tech back to historical figures, like to show my phone to Galileo or to take Leonardo da Vinci for a ride in my car. But I guess you don't need to go that far to blow minds.

Cray1 should be compared to nowadays raspberry pi pico 2 / rp2350 which has similar specs (using external ram).

Comparing against a raspberry pi 5 is kind of overkill. While a Pico 2 is close to computationally equivalent to a cray 1 now (version 2 added hardware floating point), the cray still has substantially more memory - almost 9MB vs 520k.

For parity, you have to move up to a raspberry pi zero 2, which costs $15 and uses about 2W of powerm

A million times cheaper than a cray in 2025 dollars and quite a bit more capable.

I guess I'm old because this hasn't really been that insightful of interesting observation just by itself anymore. People often talk about technological advancement of computing as if it is a force of nature whereas the amazing specs of say a rp2350 compared to the cray-1 is more of a story of the economies of scale as opposed to merely technical know-how and design. The reason a rp2350 is a few dollars is because of fabs, infrastructure, and institutional knowledge that likely dwarf the cost of producing a cray-1. I wouldn't even be surprised if someone bothered to do a similar calculation of the cost of infrastructure needed behind each cray-1 at the time that it could even be less what is needed to produce rp2350s today. The unit price of a rp2350 to consumers being so cheap (right now that fabs still want to make it) somewhat elides the actual costs involved.

Animats below said that the Cray-1 was made from discrete components. Good luck making a rp2350 from discrete components, it likely wouldn't even function well at the desired frequency due to speed of light and RF interference issues--it would likely be even worse for GHz broadcoms used in the rpi5. This means that in a post-apocolyptic future you could make another cray-1 given enough time and resources. In 20 years when the fabs have stopped making rp2350s there simply will not be any more of them.

> the Cray had about 160MFLOPS of raw processing power; the Pi has... up to 30GFLOPS. Yes... that's gigaFLOPS. This makes it almost 200 times faster than the Cray.

Imagine traveling back to 1977 and explaining to someone that in 2025 we've allocated all that extra computing power to processing javascript bundles and other assorted webshit.