🖥️ CPU Scheduling Policies

About this simulation

An operating system's CPU scheduler decides which of several waiting processes gets the CPU next. The policy it uses changes how long each process waits, without changing how much total work the CPU actually does. This scene simulates a fixed batch of processes — each with an arrival time and a CPU burst length — and replays exactly the same workload under four classic scheduling policies so you can see the trade-offs directly.

How it works

• FCFS — processes run strictly in arrival order, to completion. Simple, but a long process can make short ones wait a long time ("convoy effect").
• SJF — among processes that have arrived, the one with the shortest remaining burst runs next. Minimizes average wait time, but can starve long processes.
• Priority — the process with the highest priority (lowest priority number) among arrived processes runs next.
• Round Robin — each process gets a fixed time slice (the quantum); if it isn't finished, it goes to the back of the queue. Fair and responsive, but frequent switching adds visible re-queuing.

Controls

• Algorithm — switch scheduling policy; the Gantt timeline and queue order rebuild instantly for the same workload.
• Quantum — time slice length used only by Round Robin.
• Processes — how many processes are in the workload.
• Playback speed — how fast simulated time advances. Drag to rotate the scene, scroll to zoom.
• 🎲 New workload — generates new random arrival times, burst lengths and priorities.

Did you know?

Real operating systems rarely use a single pure policy — Linux's Completely Fair Scheduler and Windows' multilevel feedback queues blend ideas from all four approaches, adjusting time slices and priorities dynamically based on process behavior.