EAT - TLB

P = probability of hit

EAT = Effective Access Time

MA = Memory Access Time (to get data from memory)

PTA = Page Table Access Time (to get frame from page table)

RA = TLB Access Time (to get frame from TLB)

Assume MA = PTA = 10

RA = 1

Example 1:

Without TLB (Associative Registers)

EAT = MA + PTA = 10 + 10 = 20

Example 2:

With TLB assuming a hit ratio of 80

EAT = (RA + MA) * P + (RA + PTA + MA) * (1 – P) =

(1 + 10) * 0.8 + (1 + 10 + 10) * 0.2 =

8.8 + 4.2 = 13

Example 3:

With TLB assuming hit ration of 98

EAT = (RA + MA) * P + (RA + PTA + MA) * (1 – P) =

(1 + 10) * 0.98 + (1 + 10 + 10) * 0.02 =

10.78 + 0.42 = 11.2

Example 4:

Assume two levels of paging without TLB

PTA₁ = Time to access 1^st page table

PTA₂ = Time to access 2^nd page table

EAT = (PTA₁ + PTA₂ + MA) = 30

Example 5:

Assume two levels of paging with TLB and a hit ratio of 80

EAT = (RA + MA) * P + (RA + PTA₁ + PTA₂ + MA) * (1-P)

(1 + 10) * 0.8 + (1 + 10 + 10 + 10) * 0.2 =

8.8 + 6.2 = 15