# Andrew S. Tanenbaum (OS) Edition 4 Exercise 3 Question 32 (Page No. 257)

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In the $\text{WSClock}$ algorithm of Fig. $3-20(c),$ the hand points to a page with $R = 0.$ If $\tau = 400,$ will this page be removed? What about if $\tau = 1000?$

The age of page $= 2204-1213 = 991$

If $\tau = 400 \Rightarrow$It is out of the working set and was referred freshly so it will be put out.

When $\tau = 100$. At this time, the page comes under the working set.

$\therefore$ It will not be removed.

## Related questions

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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.’’ What is that attribute for the FIFO algorithm? LRU algorithm? Optimal algorithm? Give the generic algorithm for these page replacement algorithms.
Suppose that the $\text{WSClock}$ page replacement algorithm uses a $\tau$ of two ticks, and the system state is the following: where the three flag bits $V, R,$ and $M$ ... to a read request to page $4.$ Show the contents of the new table entries. Explain. (You can omit entries that are unchanged.)
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. Assume that a process is allocated $3=\text{three}$ frames, and the reference string contains page numbers from the set $0, 1, 2, 3.$
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.