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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
(KSDEV_8_Y2)(KDNET_8_Y2)
Summer 2008
Operating Systems
(Time 3 Hours)
Answer FIVE questions. Mr. G. MacSweeney All questions carry equal marks. Dr. M. O’Cinneide Mr. M. Donnelly Dr. J. Buckley Dr. A. Kinsella
1. (a) Write down the principal requirements of memory management. ( 5 Marks ) (b) In the context of memory management, what is meant by the term internal fragmentation? ( 2 Marks ) (c) What is the purpose of paging? ( 2 Marks ) (d) In paging, what is meant by a frame and a page? ( 3 Marks ) (e) In Linux, what is the purpose of virtual (swap) space? ( 2 Marks ) (f) In virtual memory, what is meant by thrashing? ( 2 Marks ) (g) What is the Resident Set? ( 2 Marks ) (h) What is a page fault? ( 2 Marks )
(a) Explain what is meant by deadlock. ( 2 Marks ) (b) In the context of deadlock, give an example of a reusable resource. ( 1 Mark ) (c) Explain the difference between deadlock avoidance and deadlock prevention. ( 2 Marks ) (d) What is meant by mutual exclusion? ( 2 Marks ) (e) Apart from mutual exclusion, state two other conditions necessary for deadlock prevention. ( 2 Marks ) (f) Suggest two possible strategies once deadlock is detected. ( 2 Marks ) (g) What is a reusable resource? Give an example. ( 2 Marks )
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
(h) Calculate the available resource vector. ( 1 Mark )
(i) 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
(a) The chmod command is used to assign permissions to files. How might you grant the file keyFile01 the following permissions using the octal notation:
- user – read, write and execute
- group – read and write
- others – read ( 3 Marks ) (b) In a multi user environment how might a user share (be able to read and write to) a subdirectory of his / her home directory with other users in the same group. Assume the user’s home drive is /home/ourUser and the subdirectory is subDir. ( 4 Marks ) (c) Apart from encrypting passwords, name another application of one-way encryption algorithms. ( 2 Marks ) (d) Write down an example of a one-way encryption algorithm. ( 1 Mark ) (e) Why is single-key encryption algorithms unsuitable for network traffic? ( 2 Marks ) (f) Name a type of encryption appropriate for network traffic. ( 2 Marks ) (g) Melissa and ILOVEYOU were two well known email viruses. Explain how they infected millions of computers. ( 4 Marks ) (h) What is a polymorphic virus and why is it so difficult to detect? ( 2 Marks )
(a) In parallel processing, what is meant by the term speedup? ( 2 Marks )
(b) Write down an expression to represent Amdahl’s Law. ( 3 Marks )
(c) Why is Amdahl’s Law often expressed as an inequality? ( 1 Mark )
(d) If a program consists of one hundred operations and fifty can be done in parallel:
(i) Calculate the speedup if there are ten processors available. ( 2 Marks ) (ii) Calculate the efficiency of the system. ( 2 Marks )
(e) What are the characteristics of a real-time operating system? ( 4 Marks )
(f) In a real-time system, explain the terms periodic task and aperiodic task? ( 4 Marks ) (g) In a real-time system, what is meant by a soft deadline? ( 2 Marks )
(a) On most Linux systems, what is the usual run-level? ( 1 Mark )
(b) Why is the default run-level never set to 0 or 6? ( 1 Mark )
(c) When might the run-level be set to 1? ( 1 Mark )
(d) What is the purpose of an independent boot loader when loading up an operating system? ( 2 Marks )
(e) Write down an example of an independent boot loader. ( 1 Mark )
(f) Why is host based processing (e.g. using telnet) not regarded as true client server computing? ( 2 Marks )
(g) What is the normal minimum client requirement in a client server processing system? ( 2 Marks )
(h) With reference to file organisation - describe serial (pile) and sequential files. State an advantage and a disadvantage of each. Write down an example of where each might be appropriate. ( 8 Marks )
(i) Apart from indexed and serial file systems, write down two other types of file organisation. ( 2 Marks )
