Memory Management and CPU Scheduling Concepts

Virtual Memory

Provides the process and kernel with a private view of its main memory

Simple Segmentation

Divides each process into several segments

Physical Address

Generated by the loader when a program is loaded into the main memory

Swapping / Memory Compaction

Process can be swapped temporary from main memory to secondary memory to make available space.

Virtual Memory Segmentation

Same as simple segmentation but has no internal fragmentation

Virtual Memory Paging

Same as simple paging but has no external fragmentation

Simple Paging

Divides the memory into several equal sized frames. It produces a small amount of internal fragmentation

Best Fit

It chooses the block closest to the requested size in partitioning

Fixed Partitioning

It produces a minimal operating system overhead

Throughput

How much work is performed by the processor

Execution Time / Burst time

Time required for a process to be executed by the CPU

Waiting time

Sum of periods spent waiting in the ready queue

Shortest Job First Algorithm

Process with the smallest execution time is chosen to the next execution

Job Queue

Contains all the processes in the system

Medium Term Scheduling

Handles swapped out processes in scheduling

Round Robin Algorithm

Involves the generation of a clock interrupt at periodic intervals

Shortest Remaining Time First

It has an estimate processing time to perform the selected function

Shortest Job First

It is the best approach to minimize the waiting time

Fairness in Scheduling

Process should be treated the same

Turnaround Time

Difference between Finish Time and Arrival Time

Short-Term Scheduling

Also known as dispatcher

Response Time

Time from submitting a request until the response is received

Process Scheduling

Act of selecting a job to be dispatched