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Bbt2103:Computer Operating Systems Question Paper
Bbt2103:Computer Operating Systems
Course:Bachelor Of Business Information Technology
Institution: Meru University Of Science And Technology question papers
Exam Year:2010
1
INSTRUCTIONS: Answer question one and any other two questions
QUESTION ONE – 30 MARKS
a. Briefly describe the following terms as used in operating system
i. Process synchronization. (2 Marks)
ii. Process (2 Marks)
iii. TLB (2 Marks)
b. What is redundant array of inexpensive disk (RAID)? (2 Marks)
c. Describe the producer and consumers problem giving suggestions of how you can implement it
using semaphores. (3 Marks)
d. Consider 10 processes A, B, C, D, E, F, G, H, I and J with run time 13, 19, 5, 16, 10, 27, 7, 24, 38
and 18 seconds respectively.
i. Calculate the turnaround times and the average waiting time if the jobs are run in that order?
(2 Marks)
ii. If the SJF algorithm is used to run the jobs, calculate the turnaround times and the average
waiting time for the jobs. (4 Marks)
e. What is unsafe state? Give an example to illustrate your answer. (2 Marks)
f. Assuming pure paging and virtual memory, with the aid of a diagram describe the three pieces of
information that are stored in a single page entry. (3 Marks)
g. Explain the difference between internal and external fragmentation. Why should they be avoided?
(4 Marks)
2
h. Consider the following preemptive priority scheduling algorithm based on dynamically changing
priorities. Larger priority numbers imply higher priority. When a process is waiting for the CPU (in
the ready queue, but not running), its priority changes at a rate ??; when it is running, its priority
changes at a rate ??. All processes are given a priority o 0 when they enter the ready queue. The
parameters ?? and ?? can be set to give many different scheduling algorithms:
i. What is the algorithm that results from ?? > ??> 0? Explain (2 Marks)
ii. What is the algorithm that results from ?? < ??< 0? Explain (2 Marks)
QUESTION TWO – 20 MARKS
a. Explain four factors to consider when choosing a scheduling algorithm. (4 Marks)
b. We have seen that round robin scheduling can be modified by listing multiple occurrences of
processes so that it gives the amount of CPU time to each process according to its priority. Consider
the following processes: Process A, B, C, D and E are created at 0, 0, 4, 4 and 6 minutes, their
runtimes are 3, 2, 2, 5 and 6 minutes and their priorities are 3, 1, 2, 1 and 4, the higher the priority
the more CPU time a process gets.
i. Construct a Gantt chart for FCFS scheduling algorithm and calculate the average waiting
time (AWT) and average turnaround time (ATT) (3 Marks)
ii. For the same set of jobs, work out the AWT and ATT if shortest remaining time next (SRTN)
algorithm is used instead. (3 Marks)
iii. If a time slice of 1 unit is used, work out AWT and ATT values for Round Robin scheduling.
(3 Marks)
iv. Using priority scheduling, work out AWT and ATT values. (3 Marks)
v. Construct a graph of algorithm versus AWT for the three jobs. (4 Marks)
QUESTION THREE – 20 MARKS
a. Briefly describe the term “message passing system” (2 Marks)
b. In distributed operating systems, what are the main similarities between RPC model and the ordinary
procedure call model? (4 Marks)
c. Explain four conditions necessary for a deadlock to occur. (4 Marks)
d. A system has four processes P1, P2, P3 P4 and three types of dedicated resources R1, R2, R3. The
existence vector is E= (3, 2, 2)
? Process P1 holds on unit of R1 and requests one unit of R2
? Process P2 holds two units of R2 and requests two units of R1 and one unit of R3
? Process P3 holds one unit of R1 and requests one unit of R2
? Process P4 holds two units of R3 and requests one unit of R1
i. Draw the corresponding resource allocation graph. (4 Marks)
ii. Explain whether the system is in a deadlock? (3 Marks)
iii. Determine whether this rate of the system is safe? (3 Marks)
QUESTION FOUR – 20 MARKS
3
a. Define the term file system. (2 Marks)
b. Explain three objectives of device management. (6 Marks)
c. Explain three factors that determine disk access time. (3 Marks)
d. Suppose the head of a moving disk with 200 tracks, numbered 0 to 199 is currently servicing in a
request at track 143 and has just finished a request at track 125. The queue of requests is kept in a
FCFS order as follows: 86, 147, 91, 177, 94, 150, 102, 175, 130. Calculate the total head movement
needed to satisfy the request in the queue using the following disk scheduling algorithms:
i. Shortest seek time first (SSTF)
ii. SCAN/Elevator algorithm
iii. First Come first Served (FCFS/FIFO)
NOTE: Moving the head between two adjacent tracks count for (one) head movement. (6 Marks)
e. Define direct memory access. Under what conditions is it useful? (3 Marks)
QUESTION FIVE – 20 MARKS
a. Describe the following memory allocation techniques stating one advantage of each. (6 Marks)
i. Paging
ii. segmentation
b. Given memory partitions of 100k, 500k, 200k, 300k and 600k (in order) how would each of the First
Fit, Best Fit and Worst Fit algorithms place process 212k, 417k 112k and 426k (in order)? Which
algorithm makes the most efficient use of memory? (6 Marks)
c. Enumerate and explain any two functions of an operating system in a computer system. Provide
practical examples to illustrate your answer. (2 Marks)
d. With the aid of diagrams describe the following file implementation methods: (6 Marks)
i. Contagious allocation
ii. Linked list allocation
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