[magicalhippo]

When dealing with async I think it is very relevant to think of exactly the points where control can be switched.

As such a regular memory read is blocking, in that control will not switch while you're doing the read (ie your not doing anything else while it's copying). This is unlike issuing an async read, which is exactly a point where control can switch.

edit: As an example, consider synchronous memory copy vs asynchronous DMA-based memory copy. From the point of view of your thread, the synchronous copying blocks, while with the DMA-based copying the thread can do other stuff while the copying progresses.