BZU PAGES: Find Presentations, Reports, Student's Assignments and Daily Discussion; Bahauddin Zakariya University Multan - Scheduling in the Operating Systems, Its Levels and Types

Scheduling:
When and which process should be assigned to CPU.

Which process is executable in system?
When and which process is assigned to the CPU.
What is the time quantum for the scheduling

There are three levels for scheduling in Operating Systems.

Long Term Scheduling
Medium Term Scheduling
Short Term Scheduling

Long Term Scheduling: In this level of scheduling Operating System manage that which process should be admitted to the system; ready or suspended ready queue. OR which process competes for the system resources. This term may also known as admission scheduling of Job scheduling.

Medium Term Scheduling: Which process should compete for CPU i.e. Scheduling for the process should move from suspended ready state.

Short Term Scheduling: Which process should assign to the CPU. It is done by the dispatcher, which carry the process from ready queue and assign it to the CPU for processing.

Graphical Representation

Attachment 687

Types of Scheduling

Preemptive Scheduling: The process is assigned to the CPU for the specific time slice OR for the specific quantum of the time so the process can be taken back to the ready queue before its completion, it is called preemptive scheduling.

Non Preemptive Scheduling: CPU can not be taken back until it completed.

Types of Short Term Scheduling

Dead line Scheduling: Here a dead line is given to the CPU within this given time OR dead line CPU should complete the process successfully.

Draw Back: System can not measure the exact time for completion of any Job.
So we depend upon the user estimation.
All the resources should be available for any process.

FIFO: This is also non preemptive. And Jobs are assigned to the CPU on the basis of the arrival of the time. This technique is rarely used in Operating Systems.