Looking ahead a little bit, we're going to see this distinction between abstraction and implementation when we talk about “gangs” of ISPC program instances. The abstraction is that we can think about ISPC functions as spawning a bunch of threads that run in parallel. The implementation is that, in reality, this illusion of multiple threads is maintained by vector instructions that run on a single thread.
Looking ahead a little bit, we're going to see this distinction between abstraction and implementation when we talk about “gangs” of ISPC program instances. The abstraction is that we can think about ISPC functions as spawning a bunch of threads that run in parallel. The implementation is that, in reality, this illusion of multiple threads is maintained by vector instructions that run on a single thread.