What is system protection in Operating System ?

What is system protection in Operating System ?

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Memory Protection:

To protect the memory from illegal jumping of instruction we need some protection method. Base Limit register & Memory Key

1-Base Limit Register: 

The simplest method of memory protection is adding two register in the CPU, “BASE” and “LIMIT” that demonstrate a range of memory to which valid references can be made.

References out side the range cause a trap to the OS.

BASE address indicate starting address of the process, and LIMIT indicate size of the process.

Memory Key:

It used in IBM 360 OS.

It is a memory protection method in which we breakup all of the memory into 2KB pages and assign a 4 bit key to each.

Reference are allowed when process key and current are match otherwise discard the reference.

§CPU Protection:

To protect the CPU for the problem such as illegal execution of instruction going to infinite loop time mechanism is used.

Time start the functioning 60 to 0 seconds.

§I/O protection:

It is a mechanism that protect the I/O devices.To protect the I/O and Hardware we must bound user functionality by implementing a mechanism called “Dual Protection (dual mode)”.

Dual mode/ Kernal Mode/ Superviser Mode:

In dual protection categorized system functionality into two part.

 MONITOR MODE & USER MODE:

Monitor mode only allows the services of OS. Where User mode allow all the services related to user.

To implement this we can add mode bit (register) if value of mode bit is 0(zero) than system will working in Monitor mode. Otherwise system will work in user mode when value is 1 (one).