LRU uses recent past behavior as an estimate of near-future use.
Accurate implementation requires timestamps, counters, stack ordering, or hardware-assisted approximations.
The optimal algorithm uses perfect knowledge of future references to choose the best victim.
It is not implementable online but serves as a benchmark for other algorithms.
Correct Answer: B. Under some algorithms such as FIFO, adding frames can increase the number of page faults
Explanation:
Belady's anomaly shows that fault count is not always monotonic with frame count for non-stack algorithms.
FIFO is the classic example that may fault more after receiving additional frames.
FIFO keeps pages in arrival order and selects the oldest resident page as the victim.
It is simple but ignores how recently or frequently a page has been used.
Correct Answer: D. The original memory reference did not complete and must execute again with the page now resident
Explanation:
A precise page fault occurs before the instruction successfully completes its required memory access.
Restarting the instruction preserves the same program behavior as if the page had already been present.
Correct Answer: C. Loading pages expected to be used soon before they are individually faulted
Explanation:
Prepaging attempts to reduce a burst of future page faults by fetching a cluster of likely useful pages.
If predictions are poor, unnecessary I/O and memory use can result.
Correct Answer: B. Providing a newly allocated page initialized with zeros when it is first needed
Explanation:
Zero-fill-on-demand creates a clean page without reading old contents from a file or swap area.
It also prevents a process from seeing data left by a previous memory owner.
Copy-on-write delays physical duplication until a process attempts to modify a shared page.
This reduces fork time and memory use when many pages remain unchanged or exec follows soon.
Correct Answer: D. Programs tend to exhibit locality of reference
Explanation:
Locality means a program repeatedly accesses a relatively small set of nearby instructions and data for a period.
Keeping that working region in memory avoids faults on most references.
Correct Answer: C. A process begins execution with none of its pages preloaded and pages arrive only after faults
Explanation:
Pure demand paging relies entirely on first references to trigger page loading.
The initial instructions may therefore cause several compulsory page faults.
Correct Answer: A. To bring required pages from backing storage into memory and manage page movement
Explanation:
The pager handles page-in and page-out operations for virtual memory.
It is more precise than treating every memory transfer as whole-process swapping.
