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 routine (s)
(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
Explanation: User applications are not allowed to perform I/O in user mode – All I/O requests are handled through system calls that must be performed in kernel mode.
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