Operating System Scheduling algorithms

• It schedules different processes to be assigned to the CPU based on particular scheduling algorithms

  Process Scheduler
• What are the 6 popular process scheduling algorithms?

  1. FIRST COME FIRST SERVE(FCFS) SCHEDULING
  2. SHORTEST NEXT JOB(SJN) SCHEDULING
  3. PRIORITY SCHEDULING
  4. SHORTEST REMAINING TIME SCHEDULING
  5. ROUND-ROBIN SCHEDULING
  6. MULTIPLE-LEVEL QUEUES SCHEDULING
• _____are designed so that once a process enters the running state, it cannot be preempted until it completes its allotted time,

  non-preemptive
• is based on priority where a scheduler may preempt a low priority running process anytime when a high priority process enters into a ready state.

  preemptive scheduling(Algorithm)
• • Jobs are executed on first come, first serve basis.
  • It is a non-preemptive, pre-emptive scheduling algorithm.
  • Easy to understand and implement.
  • Its implementation is based on FIFO queue.
  • Poor in performance as average wait time is high.

  FIRST COME FIRST SERVE SCHEDULING
• • This is also known as shortest job first, or SJF
  • This is a non-preemptive, pre-emptive scheduling algorithm.
  • Best approach to minimize waiting time.
  • Easy to implement in Batch systems where required CPU time is known in advance.
  • Impossible to implement in interactive systems where required CPU time is not known.
  • The processer should know in advance how much time process will take.

  SHORTEST JOB NEXT(SJN) SCHEDULING
• • _______ is a non-preemptive algorithm and one of the most common scheduling algorithms in batch systems.
  • Each process is assigned a priority. Process with highest priority is to be executed first and so on.
  • Processes with same priority are executed on first come first served basis.
  • Priority can be decided based on memory requirements, time requirements or any other resource requirement

  PRIORITY BASED SCHEDULING
• • _______is the preemptive version of the SJN algorithm.
  • The processor is allocated to the job closest to completion but it can be preempted by a newer ready job with shorter time to completion.
  • Impossible to implement in interactive systems where required CPU time is not known.
  • It is often used in batch environments where short jobs need to give preference.

  SHORTEST REMAINING TIME
• • ______ is the preemptive process scheduling algorithm.
  • Each process is provided a fix time to execute, it is called a quantum.
  • Once a process is executed for a given time period, it is preempted and other process executes for a given time period.
  • Context switching is used to save states of preempted processes.

  Round Robin Scheduling
• • ________ ______ are maintained for processes with common characteristics.
  • Each queue can have its own scheduling algorithms.
  • Priorities are assigned to each queue.

  MULTIPLE-LEVEL QUEUES SCHEDULING
• • Jobs are executed on first come, first serve basis.

  FIRST COME FIRST SERVE SCHEDULING
• • Easy to understand and implement.

  FIRST-COME FIRST SERVE SCHEDULING
• • Its implementation is based on FIFO queue.

  FIRST-COME FIRST SERVE SCHEDULING
• • Poor in performance as average wait time is high.

  FIRST COME FIRST SERVE SCHEDULING
• • This is also known as shortest job first, or SJF

  SHORTEST JOB NEXT SCHEDULING
• • This is a non-preemptive, pre-emptive scheduling algorithm.

  SHORTEST JOB NEXT SCHEDULING
• • Best approach to minimize waiting time.

  SHORTEST-JOB-NEXT SCHEDULING
• • Easy to implement in Batch systems where required CPU time is known in advance.

  Shortest Job Next (SJN)
• • Impossible to implement in interactive systems where required CPU time is not known.

  SHORTEST JOB NEXT AND SHORTEST TIME REMAINING
• • The processer should know in advance how much time process will take.

  Shortest Job Next (SJN)
• • ________ is a non-preemptive algorithm and one of the most common scheduling algorithms in batch systems.

  Priority Based Scheduling
• Each process is assigned a priority. Process with highest priority is to be executed first and so on

  PRIORITY BASED SCHEDULING
• • Processes with same priority are executed on _____ ____ ___ __ ___ basis

  first come first served
• Priority can be decided based on ____

  memory requirements, time requirements or any other resource requirement
• ____ is the preemptive version of the SJN algorithm.

  Shortest remaining time (SRT)
• • The processor is allocated to the job closest to completion but it can be preempted by a newer ready job with shorter time to completion.

  Shortest Remaining Time
• • It is often used in batch environments where short jobs need to give preference.

  Shortest Remaining Time
• is the preemptive process scheduling algorithm.

  Round Robin Scheduling
• • Each process is provided a fix time to execute, it is called a ______.

  quantum
• • Once a process is executed for a given time period, it is preempted and other process executes for a given time period.

  Round Robin Scheduling
• • ______ _____ is used to save states of preempted processes. (RR SCHEDULING)

  Context switching
• _____ ____are maintained for processes with common characteristics.

  Multiple queues
• • Each queue can have its own scheduling algorithms.

  Multiple-Level Queues Scheduling
• • Priorities are assigned to each queue.

  Multiple-Level Queues Scheduling