MAY 2010 Coventry University Faculty of Engineering & Computing
207SE Operating Systems and Security Instructions to candidates Time allowed:
3 hours 0 minutes
This is a Closed Book Examination Answer:
Any 4 Questions
The total number of questions in this paper: 5 All questions carry equal marks Start each question on a new page and carefully identify your answers with the correct question number For this examination you will be supplied with the following: 1 Answer Book/s
You must hand this question paper in at the end of the examination Please keep in a safe place for future reference 207SE-MAY10-QUES.DOC 207SE-MAY10-QUES. DOC
A file system supports ‘permissions’ such as execute on an individual file. List five other permissions that can be applied to a file.
b)
(5 marks)
An NTFS file system drive has been heavily used and it is expected that a defragment operation will allow an increase of 5% in the reported empty space.
Discuss in your own words what defragmentation is and how it helps in effectively managing disk space.
c)
(6 marks)
A file system is required for an organization with 1500 users. Out of 1500, 1490 belongs to same category of users and want to access one file.
Discuss how permissions can be setup on the file.
d)
(4 marks)
A file is required to be copied using a C/C++ program. Provide
pseudocode
listings
for
the
operation
highlighting all important steps. Assume you can open the file without any error.
State the differences between processes and threads in the context of computer operating systems.
b)
(6 marks)
A process makes a request to print documents to a printer. It just so happens that at the same instant another process makes a similar request.
How do you ensure that the two processes do not interfere with each others?
c)
(6 marks)
Deadlock is a serious problem that can occur in concurrent systems. How do you, as an OS designer and developer, control deadlock? In your answer, briefly explain the four conditions for
Define the term ‘virtual memory’ and explain the basic concepts behind its operation.
b)
(6 marks)
Describe in detail the mechanism by which a virtual address is translated to a physical memory address. A diagram will help to illustrate this.
c)
(8 marks)
In a particular computer system the real (physical) address is 32 bits and the virtual address is split as 10 bits ‘offset’, 2 bits ‘byte addressability’, 20 bits being left for identifying the page. What size are the Pages and the Page Table? Comment on the design choice.
d)
(6 marks)
Describe the use that is made by the OS of the ‘writtento bit’ sometimes known as the ‘dirty bit’. Where is it and what effect does it have on the performance of the system?
Justify why security is an important aspect of operating systems. State the difference between security policy and security mechanisms in the context of an operating
system.
b)
(8 marks)
A protection domain is a set of access rights defined as a set of objects and the operations permissible on them. The diagram below shows the protection domain scenario for objects: F1, F2, F3, F4, and P1. User process executing in domain D1, D2, D3 or D4 has access rights specified by each domain.
Produce an access matrix specifying the authorisation policy for the scenario below. (5 marks for the structure) (6 marks for the matrix)
