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Modern Operating Systems by Herbert...
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Page 288
CHAP. 3
PROBLEMS
257
(a) Why will the standard replacement algorithms (LRU, FIFO, clock) not be effective
in handling this workload for a page allocation that is less than the sequence
length?
(b) If this program were allocated 500 page frames, describe a page replacement ap-
proach that would perform much better than the LRU, FIFO, or clock algorithms.
28.
If FIFO page replacement is used with four page frames and eight pages, how many
page faults will occur with the reference string 0172327103 if the four frames are ini-
tially empty?
Now repeat this problem for LRU.
29.
Consider the page sequence of Fig. 3-15(b). Suppose that the
R
bits for the pages
B
through
A
are 11011011, respectively. Which page will second chance remove?
30.
A small computer on a smart card has four page frames.
At the first clock tick, the
R
bits are 0111 (page 0 is 0, the rest are 1).
At subsequent clock ticks, the values are
1011, 1010, 1101, 0010, 1010, 1100, and 0001.
If the aging algorithm is used with an
8-bit counter, give the values of the four counters after the last tick.
31.
Give a simple example of a page reference sequence where the first page selected for
replacement will be different for the clock and LRU page replacement algorithms. As-
sume that a process is allocated 3=three frames, and the reference string contains page
numbers from the set 0, 1, 2, 3.
32.
In the WSClock algorithm of Fig. 3-20(c), the hand points to a page with
R
= 0. If
τ
=
τ
=
1000?
33.
Suppose that the WSClock page replacement algorithm uses a
τ
of two ticks, and the
system state is the following:
Page
Time stamp
V
R
M
0
6
1
0
1
1
9
1
1
0
2
9
1
1
1
3
7
1
0
0
4
4
0
0
0
where the three flag bits
V
, R, and
M
stand for Valid, Referenced, and Modified, re-
spectively.
(a) If a clock interrupt occurs at tick 10, show the contents of the new table entries. Ex-
plain. (You can omit entries that are unchanged.)
(b) Suppose that instead of a clock interrupt, a page fault occurs at tick 10 due to a read
request to page 4. Show the contents of the new table entries. Explain. (You can
omit entries that are unchanged.)
34.
A student has claimed that ‘‘in the abstract, the basic page replacement algorithms
(FIFO, LRU, optimal) are identical except for the attribute used for selecting the page
to be replaced.’’
(a) What is that attribute for the FIFO algorithm? LRU algorithm? Optimal algorithm?
(b) Give the generic algorithm for these page replacement algorithms.

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