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ISRO | ISRO CS 2011 | Question 49
  • Last Updated : 11 May, 2018

Consider a 32-bit machine where four-level paging scheme is used. If the hit ratio to TLB is 98%, and it takes 20 nanosecond to search the TLB and 100 nanoseconds to access the main memory what is effective memory access time in nanoseconds?

(A) 126
(B) 128
(C) 122
(D) 120


Answer: (B)

Explanation: For 4 level Paging scheme, Effective Memory access Time, EAT =

HTLB * TTLB + (1 - HTLB)[ TTLB + 4*Tm] + Tm]

where, HTLB = hit ratio of TLB
       TTLB = search time of TLB
       Tm = Memory access time

Applying the formula:

EAT = (0.98 *20) + 0.02(20 + 400) + 100
EAT = 19.6 + 8.4 + 100
EAT = 128 ns

Option (B) is correct.

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