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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2011/
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 2011/
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) Using an appropriate example, explain what is meant by deadlock. ( 4 Marks )
(b) With reference to deadlock, what is meant by a safe state? ( 2 Marks )
(c) Consider the following system which is characterised by the Total Resource Vector and Current Resource allocation shown below.
Total Resource Vector
R1 R2 R
Current Resource Allocation
R1 R2 R P1 2 1 2 P2 1 2 2 P3 1 1 0 P4 2 1 1
Calculate the current Available Resource Vector for the system. ( 2 Marks )
(d) The following matrix describes the Total Resource Claims for each of the current processes. Is the system currently in a safe state? ( 6 Marks )
a. Total Resource Claims
R1 R2 R P1 4 3 5 P2 2 3 4 P3 6 5 7 P4 5 5 7
(e) The algorithm above describes a means of avoiding deadlock. What is the name of this algorithm? ( 1 Mark )
(f) What is the fault with this algorithm? ( 1 Mark )
(g) State four ways in which deadlock can be avoided. ( 4 Marks )
(h) Name two general approaches to avoiding deadlock. ( 2 Marks )
(i) In the context of operating systems, what is meant by a reusable resource? Give an example of a reusable resource. ( 3 Marks )
(a) Briefly define the Multilevel Feedback scheduling algorithm. ( 2 Marks )
(b) Consider the following set of processes with arrival times and service times given in milliseconds.
Process Name Arrival Time Service Time A 0 3 B 1 5 C 3 2 D 9 5 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). ( 4 Marks )
(c) For each process calculate the turnaround and the normalized turnaround times. ( 4 Marks )
(d) Apart from multi-level feedback, name three other short term scheduling algorithms. ( 3 Marks )
(e) 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 151 and is moving toward track 199. Also assume that the drive has 200 tracks numbered 0-199.
Request queue: 67, 146, 55, 161, 88, 91, 121, 181, 133 (i) Circular Look ; (ii) Scan (6 Marks)
(f) With reference to RAID, what is data striping and state an advantage of using it when writing data to disk. ( 2 Marks )
(g) With reference to RAID, what is redundancy? ( 2 Marks )
(h) Which RAID level uses no redundancy? ( 2 Marks )
(a) In operating systems, what is the purpose of a semaphore? ( 2 Marks )
(b) Using pseudo-code, describe the wait() and signal() operations on semaphores. ( 6 Marks )
(c) What is the purpose of the wait() and signal() operations? ( 4 Marks )
(d) In the context of concurrency, what is meant by starvation? ( 2 Marks )
(e) Define mutual exclusion? ( 2 Marks )
(f) State the requirements for mutual exclusion. ( 5 Marks )
(g) Why is interrupt disabling an unsatisfactory solution to the mutual exclusion problem? ( 3 Marks )
(h) What is the name of the algorithm that solves the mutual exclusion problem? ( 1 Mark )
