The Gateway to Computer Science Excellence
First time here? Checkout the FAQ!
+1 vote

I am getting answer as 88.6 time unit. 

using Total page service time = 250 x 0.94 + 0.06 x 450 = 262 time units

Access time = p( page service time + m) + (1-p)(m)  = p * page service time + m   ( p is page fault rate) 

Substituting the values i got access time = 88.6 time unit. 

but the answer is 85.6 time unit. Please point where i am going wrong. 

asked in Operating System by Junior (677 points) | 72 views
mine coming 93.1

dirty page should also considered
I think dirty page is considered in Total page falult time that i have calculated, Isn't it,

could you please explain how did you get 93.1 Please.

2 Answers

+1 vote
The average access time

(1-p)memory access time+p(memory access time+page fault service time +dirty page service time)




=93.1 time units
answered by Veteran (82.8k points)
0 votes

The question is little ambiguous because it hides various standard properties.
Now Working of virtual memory is quite complicated yet simple .
Here is the reference of page fault summary.

Now what they assumed in question is if page is dirty then complete procedure takes place in 450 unit of time {Complete this is hiding certain details}
and if now the servicing it means without updating it just fetching detail takes 250 units only.

Now :
Eqn would be :
Avg access time : Page hit *Memory access + page miss[page dirty*dirty service time+page not dirty * page fault service time]
Thus :

85.6 time units

answered by Veteran (11.8k points)

Quick search syntax
tags tag:apple
author user:martin
title title:apple
content content:apple
exclude -tag:apple
force match +apple
views views:100
score score:10
answers answers:2
is accepted isaccepted:true
is closed isclosed:true

34,239 questions
40,932 answers
39,846 users