Async Isn't the Same as Parallelism

The distinction between async and parallelism is an important one. Async is primarily about allowing other work to make progress while something is waiting. Parallelism is about performing multiple pieces of work at the same time.

And async doesn’t necessarily mean multithreaded either. Different languages and runtimes implement asynchronous execution in different ways, so you shouldn’t assume that an async operation means another thread is somewhere doing the work.

This is why async can provide concurrency without necessarily providing parallelism: multiple operations can make progress over the same period of time without their code actually executing at the exact same moment.