Operating Systems

This document provides answers to various questions related to operating systems. It covers topics such as memory mapping, memory compaction and reallocation, and different scheduling algorithms.

Running head: OPERATING SYSTEMS
Operating Systems
Name of the Student:
Name of the University:
Author Note

1
OPERATING SYSTEMS
Answer to question number B-Q1
Answer a
The address at the start of frame 1 is page 1 and the address at the end of frame 1 is
page 4.
Answer b
Yes, page 2 is mapped to frame 2.
No, page 3 is not mapped to frame 3.
Answer c
The pages which have not yet been loaded into the memory are pages 3,6,7.
Answer d
When the process A refers to an address in page 3, the paging system at first traverses
to the page 3 and looks for the address in the page. After the page is found the logical address
in the page is obtained and the corresponding address to the physical memory is also
identified. The data is then fetched from the physical address in the machine.
Answer e
Logical address
maps to
Physical address
1023 10
3000 11
4120 13
5000 12
Answer to question number B-Q2a
The process of memory compaction and reallocation is to be done as frequent as
possible. The major advantages of process are that it makes a number of memory available to

2
OPERATING SYSTEMS
the users and the available blocks are reallocated together so that the memory can be made
useful. The main disadvantage to this that the more number compaction takes place with the
increase in waiting time for the other processes. With the increase in the number of
compaction the over heading processes keeps increasing and in case where the priority of a
process is more the processor would be spending a large amount time on compaction rather
than actually processing the jobs.
Answer to question number B-Q3a
i) FCFS
ii) SJN
iii) SRT
iv) Round Robin (use time quantum of 3)
Answer to question number B-Q3b

3
OPERATING SYSTEMS
Waiting time – The waiting time is regarded as the time that is required for the processors to
ready a process for running but transferring it to the running state.
Turnaround time – The turnaround time is the total time taken for the submission of the
programs or the process required for execution and the returning the output value to the users
in the system.
FCFS
Process Burst Time Arrival Time Service Time
A 13 0 0
B 6 1 13
C 3 3 19
D 12 7 22
E 2 9 32
Average wait time – (0 + 12 + 16 + 15 + 23) = 66/5 = 13.2
Turnaround time – (13 + 18 + 19 + 27 + 25) = 102/5 = 20.4
SJN
Process Burst Time Arrival Time Service Time
A 13 0 11
B 6 1 1
C 3 3 8
D 12 7 11
E 2 9 34

4
OPERATING SYSTEMS
Average wait time – (11+0+5+4+25) = 45/5 = 9
Turnaround time – (24 + 6 + 8 + 16 + 27) = 81/5 = 16.2
SRT
Process Burst Time Arrival Time Service Time
A 13 0 36
B 6 1 9
C 3 3 3
D 12 7 17
E 2 9 3
Average wait time – (36 + 8 + 0 + 10 - 6) = 48/5 = 9.6
Turnaround time – (49 + 14 + 3 + 22 - 4) = 84/5 = 16.8
Round Robin (use time quantum of 3)
Process Burst Time Arrival Time Service Time
A 13 0 36
B 6 1 19
C 3 3 19
D 12 7 5
E 2 9 5
Average wait time – (36 + 18 + 16 – 2- 4) = 64/5 = 12.8
Turnaround time – (49 + 24 + 19 + 10 - 2) = 100/5 = 20

5
OPERATING SYSTEMS
Bibliography
[1] Hähnel, Marcus, Weidong Cui, and Marcus Peinado. "High-resolution side channels for
untrusted operating systems." 2017 USENIX Annual Technical Conference (USENIX ATC
17). 2017.
[2] Xu, Yuanzhong, Weidong Cui, and Marcus Peinado. "Controlled-channel attacks:
Deterministic side channels for untrusted operating systems." Security and Privacy (SP),
2015 IEEE Symposium on. IEEE, 2015.