Does a thread waiting on IO also block a core?

Question

In the synchronous/blocking model of computation we usually say that a thread of execution will wait (be blocked) while it waits for an IO task to complete.

Answer 1

If we assume it's not async, then I would say, in that case, your thread owning the thread would be put to the waiting queue for sure and the state would be "waiting".

Context-switching wise, IMO, it may need a little bit more explanation since the term context-switch can mean/involve many things (swapping in/out, page table updates, register updates, etc). Depending on the current state of execution, potentially, a second thread that belongs to the same process might be scheduled to run whilst the thread that was blocked on the IO operation is still waiting.

For example, then context-switching would most likely be limited to changing register values on the CPU regarding core (but potentially the owning process might even get swapped-out if there's no much memory left).