3.8k views
Consider a paging hardware with a $TLB$. Assume that the entire page table and all the pages are in the physical memory. It takes $10$ milliseconds to search the $TLB$ and $80$ milliseconds to access the physical memory. If the $TLB$ hit ratio is $0.6$, the effective memory access time (in milliseconds) is _________.

edited | 3.8k views

EMAT=TLB hit $\times$ (TLB access time $+$ memory access time) $+$ TLB miss(TLB access time $+$ page table access time+memory access time)

$=0.6(10+80)+0.4(10+80+80)$

$= 54+68$

$=122$ $msec$
by Active (4.1k points)
edited by
0
Can you please explain answer to this question in detail @Arjun Sir, @Neha pawar
+13

@ sandeep  effective memory access time = adress translation time + page access time

adress translation time  = TLB access time +  TLB miss*(memory access time)

=    10 + 0.4*80

= 42 ms

page access time        = memory access time

=80 ms

so,        effective memory access time    = 42 + 80   = 122ms

0
This kind of approach is required to question in the GATE.
0

0
Good explanation
0

@`JEET

why it is given as "Assume that the entire page table and all the pages are in the physical memory".

+1
Yes, that has to be assumed.

Let's say you don't have those things in the physical memory then there is no use of this concept itself.

In the worst-case things should be there in the physical memory to make it applicable.
+1

One more simple doubt.

TLB hit ratio 6 means, Out of 10 times, 6 times we found the frame number in TLB,  also Out of 100 times, 60 times we found frame number in TLB. Isn't ?

Then EMAT should be depend on the total number of times of access ? What i am trying to ask is " EMAT of a total of 10 access should be less than EMAT of a total of 100 access". It should vary for different number of total times of access Isn't ? Why the EMAT is fixed 122 m sec(here)?

+1

The 'effective access time' is essentially the (weighted) $\color{blue}{\text{average time}}$ it takes to get a value from memory.

TLB hit ratio means the total number of times you found the address in the tlb divided by the total number of queries to the tlb.

+1
Ok, Thanks.. Its for "a" value.. Now it is clear.