For more discussions on physical thread vs. logical thread: https://stackoverflow.com/questions/18857107/logical-thread-vs-physical-thread

I think it's actually a little misleading to talk about threads on this slide because ISPC (and SPMD) doesn't actually result in the spawning of multiple threads. The gang of ISPC program instances is actually simulated by vector instructions!

@kevtan I think the idea here is that the abstraction of considering SPMD execution as multiple instances of the function running in parallel is designed to be more compatible with the way that someone writing the code might conceptualize parallelizing the execution of their code to get better performance. This abstraction enables the programmer to think about the system as if it were executing this way, without needing to worry or have any knowledge about the vector instructions running in the background.