Question

In a virtual memory system, the I/O operations executed by a user program can be of two different types. Name them and explain when each one of them occurs.

Answer 1

Ans) In a virtual memory system, there is a dual-mode operation and there are two separate modes:- monitor mode and user mode.

Now I/O operations are executed as I/O is protected by making all I/O instructions privileged. In monitor mode, the CPU can use all instructions and access all areas of memory.The CPU automatically switches to monitor mode whenever an interrupt or trap occurs. So, the OS code is run in monitor mode.

And while running in user mode, the CPU cannot execute them; thus, user code, which runs in user mode, cannot execute them. User code requests I/O by making appropriate system calls. After checking the request, the OS code, which is running in monitor mode, can actually perform the I/O using the privileged instructions.