Question

How computer Hardware is protected, Explain Dual-Mode Operation concept for Hardware protection?

Answer 1

Answer:-

Computer hardware is protected in the following ways:-

1) Dual-Mode Operation

2) I/O Protection

3) Memory Protection

4) CPU Protection

Dual-Mode Operation

Sharing system resources requires the operating systems to ensure that an incorrect program cannot cause

other programs to execute incorrectly. Provide hardware support to differentiate between at least two

modes of operations.

   1. User mode – execution is done on behalf of a user.

   2. Monitor mode (also kernel mode or system mode) – execution is done on behalf of the operating system.

Mode bit added to computer hardware to indicate the current mode: monitor (0) or user (1).

When an interrupt or fault occurs hardware switches to monitor mode.

Privileged instructions can be issued only in monitor mode.

I/O Protection

All I/O instructions are privileged instructions. Must ensure that a user program could never gain control

of the computer in monitor mode (I.e., a user program that, as part of its execution, stores a new address in the interrupt vector).

Memory Protection

Must provide memory protection at least for the interrupt vector and the interrupt service routines. In order to have memory protection, add two registers that determine the range of legal addresses a program may access:

Base register – holds the smallest legal physical memory address.

Limit register – contains the size of the range Memory outside the defined range is protected.

Hardware Protection

When executing in monitor mode, the operating system has unrestricted access to both monitor and user’s memory. The load instructions for the base and limit registers are privileged instructions.

  

CPU Protection

1.Timer – interrupts computers after a specified period to ensure the operating system maintains control.

2.Timer has decremented every clock tick.

3.When timer reaches the value 0, an interrupt occurs.

Timer commonly used to implement time-sharing.

Time also used to compute the current time.

Load-timer is a privileged instruction.

Thanks, Hope this will help you .

Have a nice day.