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Consider a paging system with the page table in memory. Each memory reference takes $200$ ns. The TLB has hit ratio of $75 \%$ and the time to look for pages in TLB is almost negligible. What is the effective paged memory reference time in ns?

1. $400$
2. $250$
3. $150$
4. $200$

Case 1: The entry is in associative register it takes 200 ns to access the word memory. This happens 75% of time(w1). Let THIS 200 ns be c1.

Case 2: If the page is not in associative register --> 400 nanoseconds: 200 nanoseconds to access the page table and 200 nanoseconds to access the word in memory. This happens 25% of time(w2). Let this 400 ns be c2
Thus, effective access time is
= w1c1 + w2c2
= (0.75 × 200 ns) + (0.25 × 400 ns)
= 250 ns
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