Computer Systems and OS

Context Switching Simulator

Watch the CPU switch between processes. Adjust time slices and I/O waits to compare CPU efficiency and scheduling overhead.

Choose what you want to see

No setup is required. Pick a scenario and press Start.

Balanced: 5 processes share the CPU with a 4 ms time slice.

Advanced settings — optional

Processes 5

Time quantum 4 ms

Switch cost 1 ms

I/O frequency 20%

Playback speed

Watch the CPU

Live process movement

Follow the highlighted process as it gets a turn on the CPU.

Ready

Ready to begin Press Start simulation above. You can pause or move one event at a time.

WAITING FOR A TURN 0 processes

These processes are ready. The first one will run next.

NOW USING THE CPU

—

IDLE

Time slice —

COMPLETED 0 finished

Finished processes no longer need CPU time.

1. Save current process → 2. Choose next process → 3. Load and continue

Live metrics

Simulation stats

Useful work compared with scheduling overhead.

ELAPSED 0 ms

SWITCHES 0

DONE 0/5

CPU EFFICIENCY —

Recent scheduler events

What is saved?

A process must resume exactly where it stopped. The operating system therefore records the small set of CPU and scheduling data that describes its current execution state.

Program counter: the next instruction to execute
CPU registers: temporary values used by the program
Stack pointer: the current function-call and local-data position
Scheduling state: priority, status and accounting information

Quantum trade-off

The time quantum controls how long a process may keep the CPU in round-robin scheduling. There is no universally perfect value.

Very short: responsive, but produces frequent switches and more overhead
Very long: efficient for long CPU bursts, but other processes wait longer
Balanced: aims to keep interaction responsive without wasting too much CPU time

Why does I/O matter?

A process cannot usefully occupy the CPU while it waits for disk, network or user input. It moves to the Waiting state and another Ready process gets a turn.

The I/O device continues independently of the CPU
Completion makes the process Ready again
The process joins the end of this simulator's round-robin queue
If every process is waiting, the CPU becomes temporarily idle

A context switch, step by step

A timer interrupt, an I/O request, completion or an explicit yield can give the scheduler a chance to choose another process.

1. Interrupt or yield Execution enters the operating-system scheduler. → 2. Save context The current process state is stored safely. → 3. Choose next The scheduler selects the front of the Ready Queue. → 4. Restore context The selected process state is loaded into the CPU. → 5. Resume execution The process continues from its saved instruction.

How to read this simulator Blue timeline blocks are useful process execution. Orange CS blocks are context-switch overhead. A shorter quantum usually creates more orange blocks, while I/O-heavy workloads move processes between Waiting and Ready more often.

This simulator is a deterministic conceptual model. Real operating systems also consider priorities, multiple CPU cores, cache effects, interrupts and scheduler-specific policies.

For a more detailed explanation, see the blog posts: English · Korean