--- title: "Round robin scheduling (5, 8, 7 ms, q=2)" subject: "Embedded System" chapter: 6 key: "semester_6/embedded_system:sched-rr-5-8-7-q2" source: https://www.bctengineer.com/q/semester_6/embedded_system/sched-rr-5-8-7-q2 site: BCT Engineering --- # Round robin scheduling (5, 8, 7 ms, q=2) Embedded System · Chapter 6: RTOS - Asked in: 2075 Bhadra, 6 marks - Video: [Round Robin Scheduling Algorithm| Preemptive | Operating System | OS](https://www.youtube.com/watch?v=j5Rt_at1oyk) — Sudhakar Atchala - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/embedded_system/sched-rr-5-8-7-q2 - Whole chapter: https://www.bctengineer.com/md/semester_6/embedded_system/chapter-6 ## Question Three Processes P1, P2 and P3 with estimated completion time 5, 8, 7 ms respectively enters the ready queue together. Calculate WT, TAT for each process and calculate AWT and ATAT using Round Robin Pre-emptive scheduling algorithms with time slice of 2 ms. ## Short answer Round-robin with time slice 2 ms gives waiting times: P1 8, P2 11, P3 13 ms; average waiting time = 10.67 ms, average turnaround time = 17.33 ms. ## Answer Round robin (pre-emptive) with a time slice of 2 ms; all processes arrive at 0 in the order P1, P2, P3. #### Gantt chart ```text | P1 | P2 | P3 | P1 | P2 | P3 | P1 | P2 | P3 | P2 | P3 | 0 2 4 6 8 10 12 13 15 17 19 20 ``` #### Remaining time after each slice - Round 1: P1 0-2 (3 left), P2 2-4 (6 left), P3 4-6 (5 left) - Round 2: P1 6-8 (1 left), P2 8-10 (4 left), P3 10-12 (3 left) - Round 3: P1 12-13 (done), P2 13-15 (2 left), P3 15-17 (1 left) - Round 4: P2 17-19 (done), P3 19-20 (done) #### Calculation TAT = completion time - arrival time; WT = TAT - burst time. | Process | AT | BT | CT | TAT = CT - AT | WT = TAT - BT | |---|---|---|---|---|---| | P1 | 0 | 5 | 13 | 13 | 8 | | P2 | 0 | 8 | 19 | 19 | 11 | | P3 | 0 | 7 | 20 | 20 | 13 | AWT = (8 + 11 + 13) / 3 = 32/3 = 10.67 ms ATAT = (13 + 19 + 20) / 3 = 52/3 = 17.33 ms **Answer: AWT = 10.67 ms, ATAT = 17.33 ms.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. When does P1 finish? A. 8 ms B. 12 ms C. 13 ms D. 5 ms Answer: C. Its last slice is 1 ms, 12-13. (Key point: P1 completion) 2. Who finishes last? A. P2 at 20 ms B. P3 at 20 ms C. P1 at 20 ms D. P3 at 19 ms Answer: B. P3 has remaining 1 ms after P2 finishes at 19. (Key point: Last process) 3. P2's waiting time? A. 11 ms B. 19 ms C. 8 ms D. 13 ms Answer: A. TAT = 19, WT = 19 - 8 = 11. (Key point: P2 waiting) 4. AWT and ATAT? A. 17.33 ms and 10.67 ms B. 11 ms and 18 ms C. 32 ms and 52 ms D. 10.67 ms and 17.33 ms Answer: D. AWT = 32/3; ATAT = 52/3. (Key point: Averages) ## Related in Embedded System - [Round robin scheduling (6, 4, 2 ms, q=2)](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Asched-rr-6-4-2-q2) — Embedded System, chapter 6, asked 4× - [Round robin scheduling (9, 6, 3 ms, q=2)](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Asched-rr-9-6-3-q2) — Embedded System, chapter 6, asked 4× - [Round robin scheduling (53, 17, 68, 24 ms)](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Asched-rr-53-17-68-24-q4) — Embedded System, chapter 6, asked 4× - [Round robin scheduling (9, 6, 3 ms, q=3)](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Asched-rr-9-6-3-q3) — Embedded System, chapter 6, asked 4× - [Preemptive priority scheduling (4, 10, 5 ms)](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Asched-priority-4-10-5-p4) — Embedded System, chapter 6, asked 2× - [Priority and SJF scheduling with P4 and P5](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Asched-priority-and-sjf-5-process) — Embedded System, chapter 6, asked 2× ## Related in other subjects - [Real-time scheduling; two-processor numerical](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Arealtime-two-processor-fcfs-sjf-priority-rr) — Operating System, chapter 2 - [Context switching, 5-state model, MLFQ](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Acontext-switch-5state-mlfq) — Operating System, chapter 2