Multiple core processors

[John E]

And? What contradiction you can see with the said before?

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The data retrieval is done mostly by DMA mechanisms (which interface between HW buffers and RAM) that again eat no CPU. Nobody eats CPU, but data retrieval never becomes instant because of using no CPU. The freed CPU allows OS to do some other thread processing, but your thread still remains blocked

This is what I found confusing... eariler, you said:-

when your thread waits for I/O completion, the CPU just sleeps. Does it matter for you how many cores will sleep simultaneously?

I thought you meant that whenever an I/O thread (running on any core) got blocked, waiting for hardware, all the other cores would need to stop processing for some reason. Whereas what you really meant (I assume) is that any threads that are dependent on the blocked thread will also get blocked, no matter which core they're running on.