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Cork Institute of Technology
Bachelor of Science (Honours) in Computer Applications – Stage 2
Bachelor of Science (Honours) in Software Development &
Computer Networking - Stage 2
(Bachelor of Science in Computer Applications – Stage 2) (Bachelor of Science in Software Development & Computer Networking – Stage 2)
(NFQ – Level 8)
Summer 2005
Operating Systems
(Time: 3 Hours)
Instructions Answer FIVE questions. All questions carry equal marks.
Examiners: Mr. G. MacSweeny Mr. E. A. Parslow Mr. P. O’Connor Dr. D. Chambers
Q1. (a) Describe the difference between a pre-emptive and a non pre-emptive scheduling algorithm. ( 2 Marks ) (b) Give one example of a pre-emptive scheduling algorithm and one example of a non pre-emptive scheduling algorithm. ( 2 Marks ) (c) Describe the main characteristics of the following scheduling algorithms: i. Shortest Process Next ii. Shortest Remaining Time ( 4 Marks )
(d) Consider the following set of processes with duration given in milliseconds.
Process Name Arrival Time Service Time P1 0 2 P2 2 6 P3 4 3 P4 5 1
Draw a time line to show the execution of each of these processes for the two scheduling algorithms described above. For each algorithm calculate the Turnaround Time and Normalised Turnaround Time for each process. ( 8 Marks )
(e) In the context of process scheduling, distinguish between user-oriented and system-oriented criteria. ( 4 Marks )
Q2. (a) In Linux, the command useradd can be used by an administrator to create a new user. How might the potential user be supplied with a password? Describe how the administrator might also provide the user with a home directory to store his/her files. Where might this home directory be placed? ( 7 Marks )
(b) Apart from using useradd , describe two other ways of creating a user account in a standard Linux distribution. ( 3 Marks )
(c) Explain how users are authenticated when they log in to a Linux system. In your answer consider password security. ( 5 Marks )
(d) What are the security risks of a user using a simple password? ( 2 Marks )
(e) What are the different permissions in a Linux group? ( 3 Marks )
Q3. (a) Explain the following terms with respect to disk access: (i) Seek time ; (ii) Latency Time ; (iii) Transfer Time. (6 marks)
(b) For the following track request queue, describe the sequence of tracks visited for each of the following disk scheduling algorithms. Assume that the head starts at track 152 and is moving toward track 199. Also assume that the drive has 200 tracks numbered 0-199.
Request queue: 81, 149, 57, 171, 94, 99, 110, 189, 123 (i) Shortest seek time first ; (ii) Scan ; (iii) Look. (6 Marks)
(c) In the context of secondary storage, suggest how a disk manager might keep track of free space. ( 3 Marks )
(d) What is meant by internal fragmentation? ( 1 Mark )
(e) State one advantage and one disadvantage of each of the following methods of disk space allocation i. Contiguous Allocation ii. Indexed Allocation (4 Marks)
Q4. (a) Draw the Seven State Model transition diagram. In your diagram, carefully label each state and each transition. ( 14 Marks )
(b) Explain the terms: i. Mutual Exclusion ii. Concurrency iii. Starvation (6 Marks)
Q7. (a) Describe three conditions necessary for deadlock to occur. Describe one condition that characterises the occurrence of deadlock. ( 4 Marks )
(b) How is Deadlock Prevention achieved? ( 1 Mark )
(c) Outline two different types of approaches to Deadlock Avoidance. ( 4 Marks )
(d) What is meant by a safe state? ( 2 Marks )
(e) A system with 4 processes and 3 resource types is characterised by the Total Resource Vector and Current Resource Allocation shown below. Calculate the current Available Resource Vector for the system. ( 2 Marks )
Total Resource Vector
R1 R2 R 8 4 5
Current Resource Allocation
R1 R2 R
P1 2 0 0
P2 3 1 1
P3 2 1 1
P4 0 0 1
(f) The following matrix describes the Total Resource Claims for each of the current processes. Is the system currently in a safe state? Show how you derived your answer. ( 6 Marks )
R1 R2 R P1 2 4 1 P2 3 2 4 P3 3 1 1 P4 2 1 4
(g) State the major disadvantage of the Banker's Algorithm. ( 1 Mark )
