M3: Operating System (Process Scheduling Algorithm)

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Previous Job Question: Process Scheduling Algorithm

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1
Operating SystemProcess Scheduling Algorithm
A system has three processes with the following arrival times and CPU burst times:
Process Arrival Time (ms) Burst Time (ms)
P1 0 5
P2 1 3
P3 2 2
Using the First-Come, First-Served (FCFS) CPU scheduling algorithm, calculate the average waiting time and the average turnaround time.
CB, O(IT-24), 26 | Officer (IT)
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2
Operating SystemProcess Scheduling Algorithm
Why is a Circular Queue preferred over a Linear Queue in many operating systems? Explain with one example.
Combined Bank, SO(IT-24), 26 | Senior Officer (IT)

A Circular Queue is preferred over a Linear Queue because it utilizes memory more efficiently. In a Linear Queue, once the Rear reaches the last position, no new element can be inserted even if there are empty spaces at the beginning of the queue. A Circular Queue overcomes this limitation by connecting the last position to the first, allowing the freed spaces to be reused.
Advantages of Circular Queue
• Efficient utilization of memory.
• Eliminates wasted space created after deletion.
• No need to shift elements after deletion.
• Faster insertion and deletion operations.
• Widely used in Operating Systems for scheduling and buffering.
Example
In CPU Scheduling using the Round Robin Algorithm, processes are stored in a Circular Queue. After a process completes its allocated time slice (Time Quantum), it is moved to the rear of the queue, and the next process gets the CPU. This continues until all processes are executed.

Circular Queue সাধারণ Linear Queue-এর তুলনায় অধিক কার্যকর, কারণ এটি Memory দক্ষতার সাথে ব্যবহার করে। Linear Queue-এ Rear শেষ অবস্থানে পৌঁছে গেলে নতুন Element Insert করা যায় না, যদিও Queue-এর শুরুতে Delete হওয়ার কারণে খালি স্থান থাকতে পারে। Circular Queue-এ শেষ Position প্রথম Position-এর সাথে যুক্ত থাকে, ফলে খালি স্থান পুনরায় ব্যবহার করা যায়।
Circular Queue-এর সুবিধা
• Memory Utilization বেশি কার্যকর।
• Delete-এর পর তৈরি হওয়া খালি স্থান পুনরায় ব্যবহার করা যায়।
• Element Shift করার প্রয়োজন হয় না।
• Enqueue এবং Dequeue Operation দ্রুত সম্পন্ন হয়।
• Operating System-এ CPU Scheduling এবং Buffer Management-এ ব্যাপকভাবে ব্যবহৃত হয়।
উদাহরণ
Round Robin CPU Scheduling Algorithm-এ সকল Process একটি Circular Queue-তে রাখা হয়। একটি Process নির্ধারিত Time Quantum শেষ করলে সেটিকে Queue-এর শেষে পাঠানো হয় এবং পরবর্তী Process CPU পায়। এভাবে সব Process পর্যায়ক্রমে Execute হয়।
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3
Operating SystemProcess Scheduling Algorithm
Operating System Round Robin: (Quantum number =3), 4 job (job1, job2, job3, job4), Arrival time: 0,2,8,5; Burst time: 9, 7, 2, 3. What is the average waiting time?
CB, AE(IT)/AHME/SO, 21 | AME/ANE/AE

Gantt Chart:
Average Time: 25/4 = 6.25

Process	Arrival Time (ms)	Burst Time (ms)
P1	0	5
P2	1	3
P3	2	2

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Operating SystemProcess Scheduling Algorithm

Operating System (OS) scheduling is the key concept of multiprogramming. List and briefly define the major types of OS scheduling.

CB, O(IT), 20 | Officer (IT)

Major Types of Operating System (OS) Scheduling

Answer:

OS Scheduling is the process of selecting which process will execute on the CPU. It is a key concept of Multiprogramming because it improves CPU utilization and system performance.

Major Types of OS Scheduling

Scheduling Type	Definition
Long-Term Scheduler (Job Scheduler)	Selects jobs from secondary storage and loads them into main memory for execution.
Short-Term Scheduler (CPU Scheduler)	Selects a process from the ready queue and allocates the CPU to it.
Medium-Term Scheduler	Temporarily removes (swaps out) processes from memory and later brings them back to improve system performance.

The Long-Term Scheduler controls the degree of multiprogramming, the Short-Term Scheduler allocates the CPU, and the Medium-Term Scheduler manages memory efficiently through swapping.

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5
Operating SystemProcess Scheduling Algorithm
Calculate The Average Waiting Time of SJF scheduling algorithm.
Process Burst Time Arrival Time
P1 10 3
P2 1 1
P3 2 3
P4 1 4
P5 5 2

(i) Average waiting time for FCFS
(ii) Preemptive SJF
(iii) Round Robin (Quantum time: 3) scheduling algorithm
Janata, ASA, 21 | AME/ANE/AE
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6
Operating SystemProcess Scheduling Algorithm
১ (গ) নিচের সারণীটি দেখুন-
Process
Burst Time (milli second)
Priority
P1
15
3
P2
2
1
P3
4
3
P4
2
4
P5
8
2
সমস্থ process একই সাথে 0 সময়ে এসে পৌঁছে।
1. i) FCFS এবং SJF Scheduling algorithm ব্যবহার করে Gantt Chart এর মাধ্যমে process গুলোর execution দেখান।
2. ii) উপরের উভয় algorithm এর জন্য প্রত্যেকটি process এর turnaround সময় নির্ণয় করুন।
BPSC_MoHA_AP, 26 | Assistant Programmer (BPSC)
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7
Operating SystemProcess Scheduling Algorithm
Job arrival time and execution time of Operating system tasks table is given, find out
Job Arrival Time Execution Time
A 0 10
B 3 7
C 5 3
Average waiting time
(i) FCFS
(ii) Preemptive SJF
(iii) Round Robin (Quantum time: 3)
Rupali, ANE, 21 |
(i) FCFS:
(ii)SJF

(iii) Round Robin:
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8
Operating SystemProcess Scheduling Algorithm
Consider the following processes with their CPU burst times:
Process Burst Time
P1 4
P2 2
P3 8
P4 6
Assume that all processes arrive at time t = 0 and are scheduled using the Non-Preemptive Shortest Job First (SJF) scheduling algorithm.
1. Calculate the completion time of each process (P1, P2, P3, and P4).
2. Calculate the waiting time of each process and the average waiting time.
BPDB, AE(CSE),2026 | Power Sector

Process	Burst Time (milli second)	Priority
P1	15	3
P2	2	1
P3	4	3
P4	2	4
P5	8	2

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