GATE Overflow Test Series | Operating Systems | Test 2 | Question: 6

Question

For the following reference-modify ordered pair, match the following columns-
$$\begin{array}{|ll|ll|}
\hline\text{I.} & \text{(Reference bit = 0, Modify bit = 0)} & \quad \text{P.} & \text{Must write out before replacement}
\\\hline \text{II.} & \text{(Reference bit = 0, Modify bit = 1)} & \quad \text{Q.} & \text{Probably will be used again soon and need to} \\& & & \text{write out before replacement}
\\\hline \text{III.} & \text{(Reference bit = 1, Modify bit = 0)} & \quad \text{R.} & \text{Best page to replace}
\\\hline \text{IV.} & \text{(Reference bit = 1, Modify bit = 1)} & \quad \text{S.} & \text{Probably will be used again soon}
\\\hline \end{array}$$

• A. $\text{I - R, II - P, III - S, IV - Q}$
• B. $\text{I - R, II - P, III - Q, IV - S}$
• C. $\text{I - Q, II - P, III - S, IV - R}$
• D. $\text{I - Q, II - P, III - R, IV - S}$

Answer 1

When a page is referenced, due to spatial locality it is expected to be used sooner (just expectation; not a guarantee).

When modify bit is set, it means the page is modified and so must be saved to secondary storage before being replaced.

So, correct option is A.