Lab · Lecture 6

Scheduling simulator

See how each CPU scheduling algorithm decides who runs next, and check your own Gantt charts against the machine.

1
Pick an algorithm at the top. Load a slide example from the preset menu or type your own arrival and burst times.
2
Press Play under the Gantt chart. The CPU box, the ready queue and the event log explain every decision tick by tick.
3
Switch to Practice. You get a random problem, fill in the table by hand, and the simulator marks each cell.

Try this first: keep the FCFS slide preset, switch the algorithm to SJF, and watch the average waiting time drop from 17 to 3.

Algorithm

First come, first served.

The convoy effect: two short jobs wait behind one long one. Avg WT 17, avg TAT 27.

3 / 10

ID	Arrival	Burst
P1	P1 arrival time	P1 burst time
P2	P2 arrival time	P2 burst time
P3	P3 arrival time	P3 burst time

P1 P2 P3

P1P2P3idle

Speedt = 30 / 30

CPU

done

Ready queue (front first)

empty

t=30: P3 completes (CT 30). All processes complete

TAT = CT - ATWT = TAT - BTRT = first start - ATutilisation = busy / total

Process	AT	BT	CT	TAT	WT	RT
P1	0	24	24	24	0	0
P2	0	3	27	27	24	24
P3	0	3	30	30	27	27
Average				27	17	17

Context switches

Total time

CPU utilisation

100.0%

Throughput

0.10 / unit

Same processes, all six policies. RR uses q = 2.

Algorithm	Avg WT	Avg TAT	Avg RT	Switches
FCFScurrent	17	27	17	2
SJF	3	13	3	2
SRTF	3	13	3	2
Priority NP	17	27	17	2
Priority P	17	27	17	2
RR	6.33	16.33	2	6