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Normally user...

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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 not possible

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B

I/O protection is ensured by operating system routine(s)

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C

I/O protection is ensured by a hardware trap

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D

I/O protection is ensured during system configuration

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Solution

The correct option is B I/O protection is ensured by operating system routine(s)
Memory-mapped I/O requires that memory locations and I/O ports share the same set of addresses, So address bit pattern that is assigned to memory can not also be assigned to an I/O port and vice versa. I/O protection in this approach is ensured by operating systems macros and routines.

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