So the entire dev environment and any programs you have running in it only uses a single thread?

Pharo uses green threads https://www.pharo.org/features

https://en.wikipedia.org/wiki/Green_thread

That feels very limiting. It's one thing to have a program run only on one core, but you're supposed to have your entire dev environment, including editor and debugger inside the VM. Won't that end up with the env freezing on compute heavy tasks?

The runtime does the mapping, it only means IS threads aren't directly exposed.

Yes, you can lock the UI quite easily if you're not careful.

So does it use symmetric multiprocessing at all?

Green threads only mean a M:N mapping to OS threads.

Right, is the N (OS threads) == 1 in this case? It's a specific, technical way of asking if it can run parallel workloads across modern multi-core CPUs.

As far as I understand it, no parallelism at all in Pharo itself.