[Jtsummers]

Cray-1 wasn't a mainframe, it was a supercomputer. As such it was designed to push the performance envelope in a way mainframes (of the time, but even today) weren't even trying for. Mainframes were designed for transaction processing and reliability. They were substantially slower than contemporary supercomputers.

[The_Colonel]

That's true, but supercomputers are somewhat conceptually similar to GPUs, so it seems like a better comparison to illustrate technological progress. Comparing mainframes and GPUs is comparing apples and oranges.

[zifpanachr23]

This is a good analogy. If you look at a modern mainframe CPU it becomes pretty clear where the differences lie. Fewer, beefier cores with a lot of focus on cache.

Supercomputers tend to use more conventional cores, but way more of them, and connect them in a large fabric. There's a lot more focus on parallelization and horizontal scaling.

Mainframe overall compute is nowhere near a supercomputer, and you probably shouldn't be running a massive physics simulation on a mainframe, but you may get more consistency and reliability for well defined tasks.