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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2010/
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: Autumn 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) List the four conditions necessary for deadlock to occur. (4 Marks)
(b) Explain what is meant by a reusable resource. (2 Marks)
(c) Write down two examples of reusable resources. ( 2 Marks )
(d) How is Deadlock Prevention achieved? ( 1 Mark )
(e) Outline two different types of approaches to Deadlock Avoidance. ( 4 Marks )
(f) What is meant by a safe state? ( 2 Marks )
(g) 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
(h) 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
(i) State the major disadvantage of the Banker's Algorithm. ( 2 Marks )
(a) What is the purpose of the dispatcher? ( 2 Marks )
(b) Explain what is meant by long-term, medium-term and short process scheduling. ( 3 Marks )
(c) What is a suspended state? ( 1 Marks )
(d) What is the difference between pre-emptive and non pre-emptive scheduling algorithms? Give an example of each. ( 3 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 3 B 2 7 C 4 4 D 6 6
Draw a timeline to show the execution of each of these processes for the following scheduling algorithms:
Shortest Remaining Time Multi-level Feedback
For each algorithm, calculate the Turnaround Time and the Normalised Turnaround Time for each process. For 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). ( 16 Marks )
(a) What is concurrency? ( 2 Marks )
(b) List six functions of a concurrency operation. ( 6 Marks )
(c) List five areas an operating system needs to monitor when running concurrent processes. ( 5 Marks )
(d) What are the principal requirements for mutual exclusion? ( 5 Marks )
(e) Consider the following ‘busy waiting’ attempt for a mutual exclusion algorithm. Explain why this algorithm does not guarantee mutual exclusion.
/*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;
( 7 Marks )
