Question

4.which instructions should be allowed only in kernel mode? (a) disable all interrupts. (b) read the time-of-day clock. (c) set the time-of-day clock. (d) change the memory map.

Answer 1

Answer:

.

Hence the answer is (a), (c) and (d).

Answer 2

Option B) Read the time-of-day clock.

Read the time-of-day clock should be allowed only in kernel mode.

• The code running in kernel mode has full, unrestricted access to the hardware below. It has the right and authority to use any memory address and execute any CPU command.
• The code running in kernel mode has full, unrestricted access to the hardware below. It can reference any memory address and carry out any CPU command. Kernel mode is often designated for the operating system's most reliable, lowest-level operations.
• The process has limited access in the User mode, which is the default mode. The process has full access to system resources including hardware, memory, etc. in the kernel mode, which is a privileged mode.
• During normal operation, a user space application can deliberately transition to kernel mode only by using a system call like open, read, write, etc. A software interrupt/exception (SWI) is triggered each time a user programme uses the correct parameters to call one of these system call APIs.

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