[ufo]

It wouldn't run in separate cores but single-threaded can also get some measure of instruction-level parallelism.

A CPU can do more than one thing at once by computing the next instruction while it's still writing the result of the previous one. However, the CPU can only do that if it's 100% sure that the next instruction does not depend on the previous instruction. This optimization sometimes can't trigger in an interpreter, because of highly mutable variables such as the program counter or the top of the interpreter stack. Fun illustration: https://www.youtube.com/watch?v=cMMAGIefZuM&t=288s