In this section, we will take about a series of scheduling policies(sometimes called disciplines)

Workload Assumptions

We will make the following assumptions about the process, or jobs, that are running in the systems

1. Each job runs for the same amount of time
2. All jobs arrive at the same time
3. Once started, each job runs to completion
4. All jobs only use the CPU
5. The run-time of each job is known

Though unrealistic, we’ll start from here and explore them

Type of resources

• Preemptible: OS can take resource away, use it for something else and give it back later
• Non-Preemptible: OS cannot take resource away; have to wait after the resource is voluntarily relinquished

Decisions about resource

• Allocation: which process gets which resources
• Scheduling: how long process keeps resources

When to schedule?

When does scheduler make decisions?

When a process

• switches from running to waiting state
• switches from running to ready state
• switches from waiting to ready