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UGC NET CSE | July 2018 | Part 2 | Question: 54

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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?

  1. I/O protection is ensured by operating system routines
  2. I/O protection is ensured by a hardware trap
  3. I/O protection is ensured  during system configuration
  4. I/O protection is not possible
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Option (A). 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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