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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 ?(A) I/O protection is ensured by operating system routines.(B) I/O protection is ensured by a hardware trap.(C) I/O protection is ensured during system configuration.(D) I/O protection is not possible. |
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