GATE CS Applied Course

EMAT in case of Page fault


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As per GALVIN, To calculate Effective memory access time in case of page fault we used: EMAT= page fault rate*(page fault service time) + (1-page fault rate)*(memory access time) My doubt is: In case of NO PAGE FAULT, why we considered only one memory access time . Why not TWO memory accesses, one for page table + one for accessing actual byte. ? That is: Why not this formula: EMAT= page fault rate*(page fault service time) + (1-page fault rate)* (2 * memory access time)

Answers

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Jnana Bhaskar Akhil Idury Posted on Dec 03, 2019 11:14 PM

If CPU is referred to a page which is not loaded into Main Memory. Then it is known as page fault. Page fault occurs while searching for a page but not for a word. So, when CPU fetches page table and required page is missing, then OS takes charge and loads the required page from secondary memory to Main memory . The time taken for loading is known as Page Fault Service Time. After loading into main memory , fetching for a word takes negligible time compared to Page Fault Service time.

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