A virtual memory has a page size of 1K words. There are eight pages and four…
2015
A virtual memory has a page size of 1K words. There are eight pages and four blocks. The associative memory page table contains the following entries :
Which of the following list of virtual addresses (in decimal) will not cause any page fault if referenced by the CPU?
- A.
1024,3072,4096,6144
- B.
1234,4012,5000,6200
- C.
1020,3012,6120,8100
- D.
2021,4050,5112,7100
Attempted by 125 students.
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Correct answer: C
Given: page size = 1K words (1024). Associative page table shows resident pages: 0 → block 3, 2 → block 1, 5 → block 2, 7 → block 0 (so pages 0, 2, 5, 7 are present).
Rule: the page number for an address = floor(address / 1024). If the page number is one of 0, 2, 5, 7 there is no page fault; otherwise there is a page fault.
For the list 1024, 3072, 4096, 6144: page numbers are 1, 3, 4, 6. Page 1 is not resident, so a page fault occurs (on 1024).
For the list 1234, 4012, 5000, 6200: page numbers are 1, 3, 4, 6. Page 1 is not resident, so a page fault occurs (on 1234).
For the list 1020, 3012, 6120, 8100: page numbers are 0, 2, 5, 7. All these pages are present in memory, so none of these addresses will cause a page fault.
For the list 2021, 4050, 5112, 7100: page numbers are 1, 3, 4, 6. Page 1 is not resident, so a page fault occurs (on 2021).
Conclusion: the only list that will not cause any page fault is 1020, 3012, 6120, 8100 because all addresses map to pages that are resident (pages 0, 2, 5, 7).
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