NATIONAL OPEN UNIVERSITY OF NIGERIA

UNIVERSITY VILLAGE, PLOT 91, CASDASTRAL ZONE, NNAMDI AZIKIWE EXPRESS WAY, JABI, ABUJA.
FACULTY OF SCIENCES
JANUARY 2021 EXAMINATION

CIT 752 – Operating System (OS) Concepts

Credit: 2 units

TIME ALLOWED: 2 Hours

INSTRUCTION: Answer Question 1 and any other THREE (3) Questions

QUESTION 1

(a) What are the three main functions of Operating Systems, and how are they important? (4 ½ marks)

(b) With the aid of a diagram, distinguish between the Operating System Shell and the Kernel. (4 marks)

(c) Discuss two (2) advantages of Spooling Systems. (4 marks)

(d) Explain what happens when a context switching occurs? (4 ½ marks)

(e) Discuss briefly how the following pairs of scheduling criteria conflict in certain settings:

(i) CPU utilization and response time (2 marks)

(ii) Average turnaround time and maximum waiting time (2 marks)

(iii) I/O device utilization and CPU utilization. (2 marks)

(f) Multi-programming enables more than a single process to apparently execute simultaneously. How is this achieved on a uni-processor? (2 marks)

QUESTION 2

(a) State three attributes of a process. (1 ½ marks)

(b) What are the relationships between threads and processes? State four. (4 marks)

(c) A process enters the blocked state when it is waiting for an event to occur.

(i) Name two (2) events that might cause a process to enter the blocked state. (2 marks)

(ii) State the similarities among waiting, blocked and sleeping state of a process. (3 marks)

(d) How does the OS prevent a process from monopolizing a processor? (2 ½ marks)

(e) State two (2) ways by which a process can respond to a signal. (2 marks)

QUESTION 3

(a) What file access pattern is particularly suited to chained file allocation on disk? (2 marks) 

(b) Differentiate by giving three (3) examples each, the basic operations that can be performed on a File and a Directory. (3 marks)

(c) Describe the difference between external and internal fragmentation. (2 marks)

(d) Describe the four memory management schemes. (4 marks)

(e) Explain the two purposes of protecting a system. (3 marks)

(f) What do you understand by the word ‘multi-dislocation’? (1 mark)

QUESTION 4

(a) Describe is a deadlock situation. (2 marks)

(b) Give four conditions that must hold in order for a deadlock to occur. (2 marks)

(c) Describe the proof that two-phase locked systems are safe. (4 marks)

(d) What does it mean for a process to be in a Critical Section? (3 marks)

(e) State one major problem associated with Critical Section. (1 marks)
(f) Explain three properties that could guarantee a solution to the Critical Section problem. (3 marks)

QUESTION 5

(ai) What is the difference between pre-emptive scheduling and non-pre-emptive scheduling? (2 marks)
(aii) What is the issue with the latter? (1 marks)

(b) Name and explain four types of scheduling. (4 marks)

(ci) Can Indefinite Postponement occur in a system that uses a FCFS Scheduler? (2 marks)

(cii) Justify your answer. (2 marks)

(d) What is meant by a process scheduler. (2 marks)

(e) What criteria affects the scheduler’s performance? (2 marks)