It’s hard to find processors these days that aren’t multi-core. I can’t remember the last time I saw a single-core computer.

(Or are you talking about the difference between “multi-threaded execution” and “multi-core execution”? That wouldn’t make sense. Threads are how you execute code on multiple cores.)

That's what I meant; multiple operating systems threads, not hyperthreaded execution on one core.

I don't remember offhand what POV-Ray's support for multi-core execution is or was. Back in the 90's, there was PVM-POV which ran on a cluster. That's probably what you'd use if you had a dual-socket machine back then. I imagine there was probably an MPI version as well. I assume it supports multicore natively now, since practically all CPUs are multi-core now.