Not sure if I understood the concept of RR correctly.
Let's say I've got three processes ready to be CPU'd:
A – 1st priority – requires 2 minutes of CPU time;
B – 3rd priority – 5 minutes;
C – 2nd priority – 10 minutes;
So in order to calculate average turnaround time 'on paper', I can presume that quantum=1 minute and process everything according to their priorities (A-C-B, etc).
But one minute is too big for a 'real' quantum, right? Should quantum=10-100 milliseconds, will everything be switched so fast that task order becomes irrelevant? Should I assume that each job will simply consume an equal amount (1/3) of CPU time and go from there? E.g. A will end in 2*3=6 minutes, B will end in (5-2)*2+6=12 minutes and C will end in 10-2-3+12=17 minutes. Thus average tat is (6+12+17)/3=11.66? Or is this just ridiculous?
Best Answer
If processes A, B and C requires execution times as follows,
Then round robin scheduling will give you the following turn around times, If the order of priority is A followed by C followed by B.
The execution of Processes takes place as follows,
Remember order does matter in round robin scheduling because in this case the average turn around time is just (4+12+17)/3=11.