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Bca Guide Study Material Notes Gujarat University Operating System and Unix

Chapter 3 Paged Memory Allocation

1 1. Fill in the blanks.
A In paging, the section of main memory are called __________.
(Guj. Uni. March 2007)
Answer
Frames
A b. A memory access faster than main memory and slower than CPU in terms of speed is called _____________ memory.
(Guj. Uni. March 2007)
Answer
Cache
2 Define following terms.
A Page
(Guj. Uni. March 2008 Old Course)
Answer
A fixed-sized section of user’s job that corresponds to page frames in main memory.
B Virtual Memory
(Guj. Uni. March 2008 Old Course)
Answer
a Technique that allows programs to be executed even though they are not stored entirely in memory. It gives the user the illusion that a large amount of memory is available when, in fact, it is not.
C Page Fault
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Answer
A type of hardware interrupt caused by a reference to a page not resdieing in memory. The effect is to move a page out of main memory and into secondary storage o another page can be moved into memory.
D Thrashing
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Answer
A phenomenon in a virtual memory system where an excessive amount of page swapping back and forth between main memory and secondary storage results in higher overhead and little useful work.
E Overlays
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F Internal Fragmentation
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Answer
A situation in which a fixed partition is only partially used in the program. The remain space within the partition is unavailable to any other job and is therefore wasted. It contrast with the external fragmentation.
E Overlays
(Guj. Uni. March 2007)
3 Explain page replacement policies FIFO, LRU in detail.
(6 marks) (Guj. Uni. March 2007)
Answer
FIFO FIFO is based on the theory that the best page to remove is the one that has been in memory the longest. Following figure shows how the FIFO algorithm works by following a job with four pages (ABCD) as it’s processed by a system with only two available page frames. Figure also shows how each page is swaped into and out of memory and marks each interrupt with an asterisk. TH
LRU The least recently used (LRU) page replacement policy swaps out the pages that show the least amount recently, figuring that these pages are least likely to be used again in the immediate future.