I think it's still largely single-threaded. They value complete determinism: you should never get a different game state one tick later based on a CPU race condition. This is for easier debugging, repeatable testing, accurate multiplayer simulation - and also just that it fits the theme of the game, players expect to be able to design certain systems to work deterministically. This design decision has a performance cost, of course.
Still there have been major performance improvements, including parallelism-lite. And just the fact that it's mainly the same engine that ran on low-spec computers from 6 years ago means it should run very smoothly on modern machines - not all of the Moore's law improvements since then have been about parallelism.
I wouldn't say 'largely'. There are definitely single-threaded parts and if you have 64 really slow cores then you won't get 64 times as many FPS (or UPS, really) as with 1 core running at 64x speed, but that's with all software.
If you have a somewhat reasonable per-core speed, multiple cores should all be loaded with work. Personally I can't say that I've noticed it helped, but that's anecdotal and I've seen the improvements as they came in incrementally rather than in one big jump from some old single-threaded version to 1.0.
> including parallelism-lite
What does that mean? When I look it up I get results for some other game with a similar name.
> What does that mean? When I look it up I get results for some other game with a similar name.
I didn't mean to refer to any established term. I meant parallelization by breaking the game up into systems, e.g. I believe the electrical system can run completely separately to the main thread without losing the deterministic guarantees, while I would think of full parallelization as allowing each assembler or inserter to be simulated in its own thread.
Maybe there's a more established term for this? Parallelization through doing different types of things at the same time, rather than doing many copies of the same thing at the same time.
Still there have been major performance improvements, including parallelism-lite. And just the fact that it's mainly the same engine that ran on low-spec computers from 6 years ago means it should run very smoothly on modern machines - not all of the Moore's law improvements since then have been about parallelism.