운영체제 9장 연습문제

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운영체제 9장 연습문제 조선대학교 이준 교수님꺼

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Exercises
9.1 Give an example that illustrates the problem with restarting the block
move instruction (MVC) on the IBM 360/370 when the source and destination
regions are overlapping.
Answer: Assume that the page boundary is at 1024 and the move
instruction is moving values from a source region of 800:1200 to a target
region of 700:1100. Assume that a page fault occurs while accessing
location 1024. By this time the locations of 800:923 have been overwritten
with the new values and therefore restarting the block move instruction
would result in copying the new values in 800:923 to locations 700:823,
which is incorrect.
9.2 Discuss the hardware support required to support demand paging.
Answer: For every memory access operation, the page table needs to
be consulted to check whether the corresponding page is resident or
not and whether the program has read or write privileges for accessing
the page. These checks would have to be performed in hardware. A
TLB could serve as a cache and improve the performance of the lookup
operation.
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62 Chapter 9 Virtual Memory
9.3 What is the copy-on-write feature and under what circumstances is it
beneficial to use this feature? What is the hardware support required to
implement this feature?
Answer: When two processes are accessing the same set of program
values (for instance, the code segment of the source binary), then it is
useful to map the corresponding pages into the virtual address spaces

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