State the required answer precisely and then provide proper explanation. It is n

Question

State the required answer precisely and then provide proper explanation. It is not enough to provide one- word or one-line answers.

Which of the following instructions must be privileged, executable only in system mode? Provide brief justification for your answer. Remember that we would like to place minimal constraints on the user, i.e., allow maximum flexibility. Analyze each case separately.

A) Clear a memory location (byte) to all zero bits.

B) Switch from user to monitor mode.

C) Turn off interrupts.

D) Read the clock.

Thanks a lot for your help!!!

Explanation / Answer

A) Clear a memory location (byte) to all zero bits.

It can be privileged, but the OS must have to check that the process that want to clear a memory location, only clear that only memory location to zero.

B) Switch from user to monitor mode.

It can be privileged, because various user programs can be switched to monitor mode. User programs make a request for switching to monitor mode.

C) Turn off interrupts.

It can be privileged, because operating system is the one that can control the flow, between various user processes and the kernel.

D) Read the clock.

It can not be privileged, because reading of the clock do not interfere with any user processes or kernel

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