CS 162 Fall 2002
Professor Alan Jay Smith
Midterm 1
Problem 1:
Assume that the job run time distribution in a system is as follows:
run
time
8
9
10
11
12
probability
.1
.2
.4
.2
.1
Consider the following scheduling algorithms: round robin (Q=1), FCFS, SRPT, SET.
a. Predict the relative performance of these four algorithms for a system with the job run time distribution
given above. Explain (and justify) your answer. (7)
b. Considering only the realizable algorithms among those listed above, either prove that one of the above
realizable algorithms is optimal (among realizable algorithms) for this system, or design a new realizable
scheduling algorithm for jobs in this system that outperforms all of the realizable algorithms considered in
part (a), and justify (show/prove/argue convincingly) why it is better. (7)
c. Assume now that your system has two stages. In the first stage, each job is processed for some amount of
time X(i) (X(i)
Problem 2:
For the following two cases, please either show a complete safe sequence or prove that there isn't one (12)
Process
A
B
C
D
has-X
30
50
30
0
has-Y
10
80
20
70
max-needs-X
60
100
105
50
max-needs-Y
40
220
50
90
(a) available: X: 40 Y: 40
(b) available: X: 40 Y: 35
Problem 3
Interrupts, Traps, Exceptions:
a. What are traps? Give at least 2 examples and explain why they are traps. Why are traps necessary? (6)
b. What are interrupts? Give at least 2 examples and explain why they are interrupts. Why are interrupts
useful? (6)
c. What are exceptions? (3)
Problem 4:
CS162 Fall 2002 Midterm 1
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