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A paging scheme uses a Translation Look-aside Buffer (TLB). A TLB-access takes 10 ns and a main memory access takes 50 ns. What is the effective access time(in ns) if the TLB hit ratio is 90% and there is no page-fault?
  • a)
    54
  • b)
    60
  • c)
    65
  • d)
    75
Correct answer is option 'C'. Can you explain this answer?
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A paging scheme uses a Translation Look-aside Buffer (TLB). A TLB-acce...
Effective access time = hit ratio * time during hit + miss ratio * time during miss TLB time = 10ns, Memory time = 50ns Hit Ratio= 90% E.A.T. = (0.90)*(60)+0.10*110 =65
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A paging scheme uses a Translation Look-aside Buffer (TLB). A TLB-acce...
Given:
- TLB access time = 10 ns
- Main memory access time = 50 ns
- TLB hit ratio = 90%
- No page fault

To find:
- Effective access time

Explanation:
- A Translation Look-aside Buffer (TLB) is a cache that stores recently used page table entries.
- When a memory access is made, the TLB is first checked to see if the required page table entry is present.
- If the page table entry is found in the TLB (TLB hit), the translation is obtained immediately and the main memory access is avoided.
- If the page table entry is not found in the TLB (TLB miss), the translation must be obtained from the page table in main memory, incurring additional access time.

Calculating effective access time:
- The effective access time can be calculated by taking into account the TLB hit ratio and the access times for TLB and main memory.

Case 1: TLB hit
- When there is a TLB hit (90% of the time), the effective access time is equal to the TLB access time, i.e., 10 ns.

Case 2: TLB miss
- When there is a TLB miss (10% of the time), the effective access time is equal to the sum of TLB access time and main memory access time.
- Since there is no page fault, the effective access time in the case of a TLB miss is 10 ns (TLB access time) + 50 ns (main memory access time) = 60 ns.

Calculating the overall effective access time:
- The overall effective access time is the weighted average of the effective access times for the two cases, based on the TLB hit ratio.
- Given that the TLB hit ratio is 90%, the effective access time for a TLB hit contributes 90% to the overall effective access time, while the effective access time for a TLB miss contributes 10%.
- Therefore, the overall effective access time is calculated as follows:
Overall effective access time = (TLB hit ratio * Effective access time for TLB hit) + ((1 - TLB hit ratio) * Effective access time for TLB miss)
= (0.9 * 10 ns) + (0.1 * 60 ns)
= 9 ns + 6 ns
= 15 ns

Conclusion:
- The overall effective access time is 15 ns.
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A paging scheme uses a Translation Look-aside Buffer (TLB). A TLB-access takes 10 ns and a main memory access takes 50 ns. What is the effective access time(in ns) if the TLB hit ratio is 90% and there is no page-fault?a)54b)60c)65d)75Correct answer is option 'C'. Can you explain this answer?
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