The Gateway to Computer Science Excellence
First time here? Checkout the FAQ!
x
+2 votes
114 views
Consider a system with the main memory access time as 200 ns and cache access time as 10 ns. Hit ratio for
read request is 0.8 and 80% of the memory requests are for read. If write through policy is used, then the
average time considering both read and write requests is _______.
a. 169.6 ns
b. 192.4 ns
c. 78.4 ns
d. None of these
asked in CO & Architecture by Junior (851 points) | 114 views
c) 78.4??
Yes. Correct.

sir please  send  solution..

1 Answer

+2 votes
Avg time= read request ( read hit*cache access time+ read miss*(main memory+cache access time)) + write request ( main memory)

Here write request* main memory is done because of write through cache so both cache and main memory Will be updated simultaneously and since main memory has large delay we have taken it

Avg time=0.8(.8*10+.2*210)+0.2*200=80 ns

Option D

unless not mention we have to take cache access time while calculating cache miss
answered by Veteran (11.3k points)
edited by

sir 

we are taking 

Avg time= read request ( read hit*cache time+ read miss*(main memory+cache time)) + write request ( main memory).  As write-through works in multilevel(heirarchical) design.

why you have not taken cache time in solution.

yes you are correct
but in answer key  (c) is given as correct answer.
I am getting the same answer as 80, same as explained by Tesla.
OK. Thank You. Sir.
There answer is incorrect, they have to mention if main memory time is including cache time or not, if not then we add cache acess time also, you can see any gate question whenever it is not mentioned they add cache acess time in main memory time
it means by default we have to consider (hierarchical design)  is it right and here we are taking Hw = 1 when it is not given then by default we have to consider it as one am i right

@kaluti

i have taken these lines directly from hamacher,

then it means here miss penalty is not equal to sum of (T(cache) + T(memory)) then by default we have to go

hierarchical design or simultaneous one  can u little bit explain i am confused
It is hierarchical only just we are using write through policy


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

29,966 questions
37,649 answers
96,476 comments
35,291 users