Normally user programs are prevented from handling I/O directly by I/O instructions in them. For CPUs having explicit I/O instructions, such I/O protection is ensured by having the I/O instructions privileged. In a CPU with memory mapped I/O, there is no explicit I/O instruction. Which one of the following is true for a CPU with memory mapped I/O ?
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Correct answer: A. I/O protection is ensured by operating system routines.
Explanation
With memory-mapped I/O, protection comes from the OS mapping I/O addresses out of user address spaces (memory protection set up by OS routines).
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