# Made Easy Test Series:Operating System-Page Fault

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Consider a system using demand paging architecture

• it takes $3ms.$ to service page fault if either empty frame is available or replaced page is not to be modified
• takes $10ms.$ if replaced page is modified.
• Main Memory access time is $1ms.$
• and page to be replaced is modified $60$% of time.

The maximum acceptable page fault rate to get effective memory access time not more than $4ms.$ is_________(%)

Let the page fault rate be $p$, then

$\Rightarrow p \times [0.4 \times 3 ms + 0.6 \times 10 ms] + (1-p) \times 1 ms \leq 4 ms$

$\Rightarrow 6.2p = 3$

$\Rightarrow p = 48 \%$

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0
why don't you add the memory access time at the time of page fault?

b'coz in the time of page first we service the page and the access main memory.

correct me if I am wrong
2
From the time when page fault occurs to handling of the page fault is called page fault service time. That's why here no need to add memory access time

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Consider a demand paged memory system, page table is held in registers. It takes 800 nsec to service a page fault if empty page is available or replaced page is not modified and 950 nsec if the replaced page is modified, main memory access time is 120 nsec. If page to be replaced is modified 85% of time and page faultrate is 20% then average memory access time is ________. (Upto 1 decimal place)