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Cork Institute of Technology
Bachelor of Science (Honours) in Software Development – Stage 2
Bachelor of Science (Honours) in Software Development and Computer
Networking – Stage 2
(NFQ Level 8)
Summer 2007
Operating Systems
(Time 3 Hours)
Answer FIVE questions. Mr. G. McSweeney All questions carry equal marks. Dr. M. O’Cinneide Mr. M. Donnelly Dr. J. Buckley Dr. A. Kinsella
Q1. (a) Distinguish between the task of the Long Term Scheduler, Medium Term scheduler and the Short Term Scheduler. ( 3 Marks ) (b) Describe criteria that might be used to evaluate different scheduling algorithms used by a Short Term Scheduler. ( 5 Marks ) (c) Describe the main characteristics of the following scheduling algorithms: Shortest Remaining Time Round Robin ( 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. The time slice for Round Robin = 2.
For each algorithm calculate the Turnaround Time and Normalised Turnaround Time for each process. ( 8 Marks )
Q2. (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, calculate the head movement required 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: 86, 147, 91, 177, 94, 150, 102, 175, 130 (i) Shortest seek time first ; (ii) Scan (4 Marks) (c) With the aid of a diagram, describe the method of disk space allocation used in UNIX. Describe how the method manages both small and large files. (7 Marks) (d) How might you calculate the size of the largest file one could allocate using the UNIX addressing method if each block is 1K and can hold 256 block addresses? (3 Marks)
Q3. (a) Draw a Process State Transition Diagram with suspended states. In your diagram, carefully label each state and each transition. ( 8 Marks ) (b) What events are likely to lead to a process switch? ( 3 Marks ) (c) Outline the steps involved in a process switch. ( 4 Marks ) (d) Apart from normal completion, suggest five reasons why a process might be terminated. ( 5 Marks )
Q4. (a) What is meant by Mutual Exclusion? ( 2 Marks ) (b) List five requirements that must be met to support Mutual Exclusion. ( 5 Marks ) (c) Using pseudocode, describe Dekker’s Second Attempt to this mutual exclusion algorithm. ( 5 Marks ) (d) Name four advantages of using UNIX as an operating system. ( 4 Marks ) (e) Describe briefly the four types of threat that can be made to a computer system. ( 4 Marks )
Q6. (a) In Memory Management, explain the terms (i) Static Partitioning (ii) Dynamic Partitioning ( 4 Marks ) (b) Why is static partitioning no longer used? ( 2 Marks ) (c) State three placement algorithms for dynamic partitioning. (3 Marks) (d) Explain what is meant by an overlay. (3 Marks) (e) What is meant by the terms page and frame? (4 Marks) (f) Explain what is meant by (i) Internal Fragmentation (ii) External Fragmentation ( 4 Marks)
Q7. (a) What is the Resident Set? ( 2 Marks ) (b) In Virtual Memory, what is a Page Fault? ( 2 Marks ) (c) Describe the steps involved in Page Fault Handling. ( 4 Marks ) (d) What does Thrashing mean? ( 2 Marks ) (e) One of the characteristics of a real-time operating system is determinism. What is meant by determinism? ( 3 Marks ) (f) Name three other characteristics of real-time operating systems. ( 3 Marks ) (g) In a real-time operating system, what is the difference between Periodic and Aperiodic tasks? ( 4 Marks )
