Scheduling Algorithm is divided into mainly 2 parts.

• Pre-emptive.
• Non-pre-emptive.

Scheduling algorithms

• It is the way of selecting the process from the ready queue and putting it into the CPU.
• According to the degree of multiprogramming, we try to keep multiple processes on the ready queue. So we can utilize the CPU in the proper way.

Pre-Emptive:

• In the pre-emptive process, the process can be sent back to the ready state from the running state. Due to many conditions like time quantum or priority.
• This is used to achieve a multiprocessing environment.

Non Pre-Emptive:

• In non-pre-emptive the process that has been sent to the running state from the ready state will not come back to the ready state, after reaching the running state, it will be executed completely and get terminated.
• This approach is generally used in the Batch operating system.

Algorithms

• Both pre-emptive and non pre-emptive processes have different types of algorithms.

• Pre-emptive:

  • SRTF (Shortest remaining time first)
  • LRTF (Longest remaining time first)
  • Round Robin.
  • Priority based.

• Non pre-emptive:

  • FCFS (First come first serve)
  • SJF (Shortest job first)
  • LJF (Longest job first)
  • HRRN (Highest response ratio next)
  • Multilevel queue/ multilevel feedback queue.

Note: From the next lecture we will see each scheduling algorithm one by one, Any feedback and suggestion welcome.