| PID | Arrival | Burst | Priority |
|---|---|---|---|
| P1 | 0 | 7 | 2 |
| P2 | 2 | 4 | 1 |
| P3 | 4 | 1 | 3 |
| P4 | 5 | 4 | 2 |
- Completion Time (CT): time when a process finishes.
- Turnaround Time (TAT): CT − Arrival.
- Waiting Time (WT): TAT − Burst.
- Response Time (RT): FirstStart − Arrival.
- Makespan: end time of the final segment.
- CPU Utilization: BusyTime / Makespan × 100.
- Throughput: Completed / Makespan.
- Context switch time: inserted between different processes.
- Select an algorithm from the dropdown.
- Enter time quantum if you choose Round Robin.
- Optionally set context switch overhead in time units.
- Add process rows and provide arrival, burst, and priority.
- Press Submit & Calculate to generate outputs.
- Use CSV/PDF buttons to export metrics and the Gantt timeline.
Engineering value of CPU scheduling metrics
Scheduling choices shape latency, throughput, and energy in embedded controllers, servers, and test rigs. This calculator reports waiting, turnaround, and response times per process, plus averages for fast comparison. CPU utilization shows how much of the makespan is productive execution versus idle gaps and context switching. Throughput, reported as completed processes per time unit, helps compare different workloads. The per-process table highlights outliers that drive user-visible jitter. Capturing these numbers across revisions creates an objective performance baseline.
Algorithm selection data you can interpret quickly
FCFS is simple but can amplify delays when long bursts arrive early. SJF and SRTF favor short bursts, often reducing average waiting time for mixed jobs. Priority scheduling represents service classes; preemptive priority improves responsiveness for critical work but can starve low-priority tasks without careful tuning. Round Robin enforces fairness using a quantum, making it practical for interactive or shared lab systems. Running the same table across algorithms makes tradeoffs measurable and easier to communicate.
Why context switch overhead matters
Task switches incur real costs: register saves, cache disruption, pipeline flushes, and scheduler bookkeeping. The overhead input inserts explicit CS segments so you can see how parameter changes affect utilization and completion time. Too-small quantum values increase switching frequency, while heavy preemption in SRTF or priority can inflate turnaround. Modeling overhead also helps compare platforms where interrupt latency or cache size differs.
Gantt timelines support verification and reporting
The timeline is a verification artifact. It shows when each process starts, pauses, and completes, including idle periods and overhead. First-start times validate responsiveness targets, and completion times validate batch windows or soft deadlines. CSV and PDF exports provide traceable evidence for reports, lab notebooks, and regression tracking.
Practical workflow for experiments
Load the example dataset, then adjust arrivals and bursts to match traces or synthetic scenarios. Compare at least three policies: fairness-focused Round Robin, latency-focused SRTF, and policy-focused Priority. Record summary metrics, then sweep quantum and context switch overhead to find stable regions where utilization stays high and response remains acceptable. Export each run to keep a clear change log for stakeholders reliably. This turns scheduling into a repeatable engineering experiment.
FAQs
1) What inputs are required for each process?
Enter a process ID, arrival time, burst time, and an optional priority value. Burst time must be greater than zero. Arrival and priority can be any integers you use consistently.
2) How is waiting time calculated?
Waiting time equals turnaround time minus burst time. Turnaround time is completion time minus arrival time. This matches common operating-systems analysis and works for both preemptive and non-preemptive schedules.
3) What does “response time” mean here?
Response time is the delay from arrival until the process first starts executing. It captures perceived responsiveness in interactive workloads and is useful when preemption or time slicing is enabled.
4) Why do I see IDLE or CS blocks in the Gantt chart?
IDLE appears when no process has arrived or all ready processes finished. CS represents context switch overhead you configured. Both reduce utilization and can increase overall completion time.
5) How should I choose a Round Robin quantum?
Pick a quantum that balances fairness and overhead. Small quanta improve responsiveness but increase context switching. Larger quanta reduce overhead but can make short tasks wait longer behind large bursts.
6) Can I use this for real-time deadline scheduling?
This tool models common general-purpose CPU schedulers. You can approximate deadlines by checking completion times against required limits, but it does not implement EDF or RMS priority assignment automatically.