Scheduling

• Scheduler 


  Manages which process to execute next and the length of time the next process can execute for
• Ready queue


  waiting to get the attention of the CPU
• Running state


  Running in the CPU
• After running in the CPU


  Finishing executing completely and leave the system.

  Get blocked, as it requires an input or output command, meaning it can’t continue until more data is received.

  Run out of time, Given a certain amount of time then suspended and moved to the back of the ready queue.
• First come First serve


  Processes are executed in the order they arrive. If a process takes a long time, the others behind must simply wait.
• Shortest job first


  Picks the processes that takes the shortest amount of time and runs them until they finish.
• Round robin


  Each process is allocated a fixed amount of time, known as a time slice. if it is not completed by the end of the time slice, it returns to the back of the ready queue.
• Shortest remaining time


  Similar to shortest job first. However, Shortest remaining time is a pre-emptive Algorithm, meaning the process can be suspended if a higher priority process Joins the queue.
• Process blocking


  While a process is running, it requires data from the hard disk. The hard disk drive is slow compared to the CPU, so the process is blocked until this input request has been serviced. When it receives the data it needs and generates an interrupt to let the scheduler know it can rejoin the queue.
• Multi-level feedback queue 


  Separates processes into multiple ready queues based on their processing needs.