BN104 Operating Systems

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08-07-2021

Question:

Attempt the Assignment 1 quiz after Week 6, and paste below the Moodle summary of your result.

Compare and contrast internal fragmentation and external fragmentation (explain with simple example, do not use the example from the lecture). In your opinion, which one might be preferred over the other. Give reason for your answer (word limit 150 words).

Memory compact/relocation is done for using the memory efficiently. In your opinion, how often should memory compaction/relocation be performed What do you think the advantages and disadvantages would be of performing it even more often (Word limit: 100 words).

You must provide references and cite the sources if you consult any external source for this task.

Given the following loading times, determine in which order the pages are replaced by the FIFO algorithm (explain your reason).

Describe how the simplified version of LRU works. Using the given values in table below for the Referenced and Modified bits, determine in which order the pages are replaced by the simplified LRU algorithm and explain why you think so.

Page	Referenced Bit	Modified Bit
Page 0	0	1
Page 3	0	0
Page 6	1	0
Page 8	0	0
Page 12	1	1
Page 14	1	0
Page 16	1	0
Page 18	1	1

Process Management and Scheduling

Given the following arrival time and CPU cycle times.

Job	Arrival Time	CPU cycles required
A	0	11
B	2	13
C	5	5
D	7	1
E	13	3

Draw a timeline for each of the following scheduling algorithms and also show the details of the ready queue formation during the time line.

i) FCFS

ii) SJN

iii) SRT

iv) Round Robin (use time quantum of 3)

Using either internet resources or books, understand the concept of waiting time and turnaround time. Define those terms (waiting time and turnaround time) in your own words. Then calculate turnaround time for every job for all four scheduling algorithms mentioned in B-Q2-a (Details of the calculations is essential).

You must provide references and cite the sources that you consulted for this task.

Answer:

The comparison between the internal and external fragmentation

EXTERNAL FRAGMENTATION	INTERNAL FRAGMENTATION
The external fragmentation occur due to the allocation of the variable sized memory to the processes.	The internal fragmentations take place due to the allocation of the fixed sized memory to the processes.
The external fragmentations occur due to the removal of certain processes of variable size from the memory of the system.	The internal fragmentations take place due to the allocation a process which is smaller in size than the fixed amount of memory and leaves a gap in the memory.
For the resolution of the external fragmentation the paging, segmentation and the compaction techniques are applied.	The best fit method is used for solving the internal fragmentations.

The relocation techniques are used before the running phase of the process starts. The lower most address of the file starts from zero. The object codes are to be adjusted so that the addresses that are appropriate can be used in the runtime.

TIME

100

105

120

The order of the pages that are to be replaced are: 3,16,8,1,18,4,15,12.

The status bits are very useful for the implementation of the LRU techniques. The status bit denotes the new entries to the system and also checks in the entries are valid or not. The least recently used entries are removed from the memory.

The order in which the pages would be replaced are: 18,12,8,3,0,16,14,6.

FCFS
SJN
SRT
Round Robin

Total time taken by a job is known as the turnaround time. The total time that the job has to wait before being executed is known as the total waiting time.

i) FCFS

A= 11-0=11

B=24-2=22

C=29-5=24

D=30-7=23

E=33-13=20

TOTAL TURNAROUND TIME= (11+22+24+23+20) = 100

AVERAGE TURNAROUND TIME=(100/4)=25

ii) SJN

A= 20-0=20

B=33-2=31

C=9-5=4

D=1=1

E=4=4

TOTAL TURNAROUND TIME= (20+31+4+1+4)= 60

AVERAGE TURNAROUND TIME=(60/4)=15

iii) SRT

A= 25-15+2-0=12

B=5-2=3

C=11-6-5=0

D=8-7=1

E=33-13=20

TOTAL TURNAROUND TIME= (12+3+0+20)= 35

AVERAGE TURNAROUND TIME=35/4)=8.75

iv) Round Robin

A= 29-0=29

B=33-2=31

C=21-5=24

D=10-7=3

E=13-13=0

TOTAL TURNAROUND TIME= (29+31+24+3+0)= 87

AVERAGE TURNAROUND TIME=(87/4)=21.75

Bibliography

[1] Moraru, I., Andersen, D.G., Kaminsky, M., Tolia, N., Ranganathan, P. and Binkert, N, November. Consistent, durable, and safe memory management for byte-addressable non volatile main memory. In Proceedings of the First ACM SIGOPS Conference on Timely Results in Operating Systems (p. 1). ACM., 2013.

[2] Sirohi, A., Pratap, A. and Aggarwal, M. Improvised Round Robin (CPU) Scheduling Algorithm. International Journal of Computer Applications, 99(18), pp.40-43., 2014.