Match the following page table bits used in virtual memory management with…
2008
Match the following page table bits used in virtual memory management with their correct functions.
List I (Page Table Bit) | List II (Function) |
|---|---|
I. Dirty bit | a. Indicates whether the page has been modified and must be written back to disk |
II. R/W bit | b. Controls access permissions (read/write protection) |
III. Reference bit | c. Used by page replacement algorithms to track page usage |
IV. Valid bit | d. Indicates whether the page is currently present in main memory |
Choose the correct matching.
- A.
I-d, II-a, III-b, IV-c
- B.
I-b, II-c, III-a, IV-d
- C.
I-c, II-d, III-a, IV-b
- D.
I–a, II–b, III–c, IV–d
Attempted by 172 students.
Show answer & explanation
Correct answer: D
Correct mapping: I → Dirty = write-back policy; II → R/W = page protection; III → Reference = page replacement policy; IV → Valid = page initialization.
Dirty: Indicates whether the page has been modified since it was loaded. If set, the page must be written back to disk before being replaced, so this bit is used for the write-back policy.
R/W (Read/Write): Specifies access permissions (read-only or read/write). This bit enforces page protection by preventing unauthorized writes when cleared.
Reference: Set when the page is accessed; used by page replacement algorithms (for example, second-chance or approximations to LRU) to decide which page to evict.
Valid: Indicates whether the page is currently present and initialized in physical memory. A cleared Valid bit causes a page fault and triggers page initialization or loading.
Therefore the correct pairing is: I - write-back policy; II - page protection; III - page replacement policy; IV - page initialization.