doubt about privileged or non privileged instruction.

Question

Talk about the correctness of following claims.

1) The instruction to switch to kernel mode is an example of a privileged instruction.

2) The instruction to switch to user mode is an example of a privileged instruction.

Detailed explanation is needed.

Answer 1

There are basically 2 modes in which a modern OS works.

User mode and kernel mode.

Whenever the the system boots ,OS transfers control to kernel mode , where kernel runs all the necessary routines and then kernel switches to user mode.

User mode allows users to run any programs of their choice .

However if there are any instructions that could alter some parts of OS or any of your resources ,IO systems ,they are marked “PRIVILEGED”

These instructions are allowed to be run only in kernel mode

Kernel then executes such instructions and returns control to User (Depends on the type of the privilege instruction)

Comments

https://www.quora.com/What-is-a-privileged-instruction-in-an-operating-system

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Hello harikesh.
Thanks for the answer and i know what do kernel mode and user mode mean.
but i asked , what kind of instruction causes switch from user to kernel mode or vice versa.

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Hello Sir.

I already went through this all. But if you put some more light , may be i would be able to tell you , where do i actually have doubt.

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http://minnie.tuhs.org/CompArch/Lectures/week05.html