Can you use one hundred percent of IO and CPU at the same time?

Question

a question that a co-interviewer asked in interviews. I always thought it was a silly question.

Assume single processor and not dual core.

Answer 1

Yes you can if DMA is not available. In that case you could end up using the CPU to move data around from I/O to I/O through central memory, if the I/O bandwidth on both devices is high enough you will effectively saturate the CPU.

Answer 2

Yes. Simple have two processes running, one that uses all CPU, and the other that uses all the I/O it can. This will do it. The real issue is what I/O is being talked about. There are a number of busses in any system, and they all can be bound at any given time.

Answer 3

I'd also look for places where IO devices are virtualized and encrypted. This is probably an unusual case, but not an impossible case.

Answer 4

Yes, you can!(Sounds like a cliche right?) But really, there is such thing as non blocking IO. You can do a lot of things while you data using up 100% IO.