UNIVERSITY EXAMINATIONS: 2012/2013
EXAMINATION FOR THE BACHELOR OF SCIENCE IN
INFORMATION TECHNOLOGY
BIT 2303 DISTRIBUTED SYSTEMS
DATE: AUGUST, 2013 TIME: 2 HOURS
INSTRUCTIONS: Answer Question ONE and Any Other TWO Questions
QUESTION ONE: 30 MARKS (COMPULSORY)
a) Define a Distributed System (2 Marks)
b) By use of well labeled diagrams illustrate three key differences between distributed
systems and centralized systems (6 Marks)
c) Differentiate between NOS (Network Operating Systems) and DOS (Distributed
Operating Systems) (6 Marks)
d) State and briefly explain four security goals, highlighting the threats to these goals
(6 Marks)
e) Outline Four advantages of replication in Distributed Systems (4 Marks)
f) Discuss how the following clock synchronization centralized algorithms work to
achieve external synchronization. (6 Marks)
i) Cristain algorithm
ii) Berkeley algorithm
QUESTION TWO: 20 MARKS
a) Discuss four advantages of Distributed Systems over Centralized Systems.
( 4 Marks)
b) Briefly describe all the components of a Distributes System (6 Marks)
c) Discuss the four models of middleware (4 Marks)
d) Describe the following models of Distributed Systems (6 Marks)
i) Client-Server Model
ii) Peer-to-Peer Model
QUESTION THREE: 20 MARKS
a) Explain the relation between an error, a fault and a failure (2 Marks)
b) State and briefly explain four drawbacks of Distributed Systems (4 Marks)
c) Describe any three desirable features of a Message Passing System. (6 Marks)
d) With the help of a clearly labeled diagram illustrate the implementation of the RPC
mechanism. (8 Marks)
QUESTION FOUR: 20 MARKS
a) Define the term reliability (2 Marks)
b) A fault causes failure of a system. Define the term fault giving two types of a fault.
(6 Marks)
c) Differentiate between the following terms in reference to reliability (6 Marks)
i) Fault avoidance
ii) Fault tolerance
d) Describe the following forms of transparencies showing their importance in
Distributed Systems (6 Marks)
i) Migration Transparency
ii) Replication Transparency
iii) Access Transparency
QUESTION FIVE: 20 MARKS
a) Differentiate between external synchronization and internal synchronization
(4 Marks)
a) Discuss the following replication approaches. (6 Marks)
i) Active replication
ii) Passive replication
b) Briefly discuss the meaning of the following terms in the context of parallel and
Distributed Systems. (4 Marks)
i) Mutual exclusion
ii) Dependability
iii) Availability.
iv) Name space
c) Describe using diagrams three algorithms for achieving mutual exclusion
(6 Marks)
