Operating system

50-percent rule in operating system

Statistically N allocated block, Another 0.5 N blocks will be lost to fragmentation. The 1/3 of memory is unusable. It is called 50 - Percent Rule

Why are page sizes always powers of 2?

Recall that paging is implemented by breaking up an address into a page and offset number. It is most efficient to break the address into X page bits and Y offset bits, rather than perform arithmetic on the address to calculate the page number and offset. Because each bit position represents a power of 2, splitting an address between bits results in a page size that is a power of 2.

Explain the basic functions of process management

The basic functions of the process management are :

• Allocating resources to processes,
• enabling processes to share and exchange information,
• protecting the resources of each process from other processes and
• enabling synchronization among processes.

What is pre-emptive and non-preemptive scheduling?

Tasks are usually assigned with priorities. At times it is necessary to run a certain task that has a higher priority before another task although it is running. Therefore, the running task is interrupted for some time and resumed later when the priority task has finished its execution. This is called preemptive scheduling.

Eg: Round robin

In non-preemptive scheduling, a running task is executed till completion. It cannot be interrupted.
Eg First In First Out