Interview Q&A / Operating Systems
Operating Systems interview questions
Processes, threads, scheduling, memory and deadlocks, in plain words.
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- What are the FCFS, SJF, Round Robin and Priority CPU scheduling algorithms, and how do you calculate waiting time?
FCFS runs processes in arrival order, SJF picks the shortest job next and gives the lowest average waiting time, Round Robin gives each process a fixed time slice in turn for fair response, and Priority runs the most important process first but can starve low-priority ones unless aging is used.
IntermediateIn-depth4 min read - Burst times 24, 3 and 3, all arriving at time 0, with a time quantum of 4 ms. What is the average waiting time under Round Robin?
P1 runs 0-4, P2 4-7, P3 7-10, then P1 alone finishes at 30. Waiting times are P1 6, P2 4, P3 7, so the average is 17 / 3, about 5.67 ms.
IntermediateQuick answer1 min read - How does the time quantum affect Round Robin performance?
A very large quantum makes Round Robin behave like FCFS. A very small one wastes time on context switches. A good quantum is longer than most CPU bursts, often cited as 80% of bursts finishing within one quantum.
IntermediateQuick answer1 min read