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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2012/
Module Title: Operating Systems
Module Code: SOFT 7006
School: Mathematics & Computing
Programme Title: Bachelor of Science (Honours) in Software Development – Year 3 Bachelor of Science (Honours) in Software Development & Computer Networking – Year 2
Programme Code: KSDEV_8_Y KDNET_8_Y
External Examiner(s): Mr. Aidan.F. Quilligan Internal Examiner(s): Mr. G. McSweeney
Instructions: Answer four questions. All questions are worth equal marks.
Duration: 2 Hours
Sitting: Winter 2012/
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination. If in doubt please contact an Invigilator.
(a) What are the conditions for deadlock to occur? ( 4 Marks )
(b) A system with four processes and three resource types is characterised by the Total Resource Vector and Current Resource Allocation as follows:
Total Resource Vector R1 R2 R 7 7 7
Current Resource Allocation R1 R2 R P1 2 0 3 P2 1 3 2 P3 2 1 2 P4 1 1 0
Calculate the available resource vector. ( 3 Marks )
(c) The following matrix describes the Total Resource Claims for each of the current processes. Is the system currently in a safe state? Explain how you derived your answer. ( 6 Marks )
R1 R2 R P1 5 2 4 P2 5 3 6 P3 3 3 2 P4 7 7 7
(d) Describe how the Multilevel Feedback scheduling algorithm works. ( 4 Marks )
(e) Consider the following set of processes with arrival times and service times given in milliseconds. Process Name Arrival Time Service Time A 0 4 B 1 8 C 3 2 D 10 6 E 12 5
Draw a timeline to show the execution of each of these processes using Multilevel Feedback Queue with queues numbered 1-4, quantum = 2i, where i is the queue level number and processes are initially placed in the first queue (i.e., level 1). Calculate the turnaround and normalized turnaround times. ( 8 Marks )
(a) In the context of disk scheduling, explain the terms seek time, latency time and data transfer time. ( 3 Marks )
(b) Why might seek time be faster on cylinders? ( 2 Marks )
(c) Draw a time line to indicate the sequence of tracks visited for the SCAN and CIRCULAR-LOOK algorithms for the following requests:
48, 106, 154, 37, 164, 123, 89, 74
Assume the firs track on the disk is 0 and the last track is 199. The last track visited was 157 and the head is moving towards 199. ( 6 Marks )
(d) Apart from SCAN and CIRCULAR-LOOK, name two other disk scheduling algorithms. ( 2 Marks )
(e) Name one advantages of using RAID. ( 2 Marks )
(f) With reference to RAID, explain the terms redundancy, data stripping and mirroring. ( 3 Marks )
(g) Write down one advantage and one disadvantage of redundancy. ( 2 Marks )
(h) In RAID 2, explain how parity bits are used to check for errors. ( 2 Marks )
(i) How does RAID 3 determine parity bits? ( 1 Mark )
(j) Why is RAID 0 sometimes not regarded as a real RAID? ( 2 Marks )
(a) Define mutual exclusion. ( 2 Marks )
(b) Name the requirements for mutual exclusion. ( 5 Marks )
(c) Consider the following code as a solution to the mutual exclusion problem:
/*Process0 / while (flag[1]) do {/ nothing /} flag[0] = true; /critical section */ flag[0] = false;
/*Process1 / while (flag[0]) do {/ nothing /} flag[1] = true; /critical section */ flag[1] = false;
Explain this algorithm. ( 4 Marks )
(d) Why does the algorithm in (c) does not guarantee mutual exclusion. ( 6 Marks )
(e) Explain why in Linux, passwords are regarded as being secure. ( 3 Marks )
(f) With relevance to Linux passwords, what is a salt and what is its purpose. ( 3 Marks )
(g) How might one validate the integrity of a package e.g. one that’s downloaded off an open network. ( 2 Marks )
