Scheduling

The act of chosing which process to run next after the previous process blocks , terminates or is forcably preempted.

Non-preemptive scheduling

A process keeps the CPU until it treminates or blocks.

Preemptive Scheduling

The process is interrupted after a certain ammount of time, called the ‘time quantum’ or ‘time slice’.

Starvation

A process is ‘starved’ if it doesn’t recieve cpu for a long time.

Priorities

Static priority

priority determined by the user for each process.

Dynamic priority

Priority determined by the system.

Algorithms

First-Come-First-Served

Ready processes are pushed onto the end of a queue, and popped of the head and run.

Round-Robin

Same as FCFS, but processes are forcably preempted after the fixed time quantum.

Shortest Job First

Run the job with the lowest time requirements first.

Multilevel Feedback Queues

Have multiple queues, with diferent, increasing priority. when a process uses all of it’s time slice, (ie. is forcably preempted), move it to a higher queue. Only run processes from a queue when lower queues are empty.