Question

Consider a paging system in which the hit ratio is 80%, TLB (Translation Look Ahead Buffer) access time is 100 nanoseconds, and main memory access time is 100 nanoseconds. Find Effective Access Time (EAT), assuming page-table lookup takes only one memory access.

• A. 20 nanoseconds
• B. 220 nanoseconds
• C. 120 nanoseconds
• D. 2 nanoseconds

Hint:

When calculating Effective Access Time (EAT) for paging systems, remember to account for both TLB hits and misses using the appropriate hit ratio and access times.

Answer 1

The Correct Option is C

Effective Access Time (EAT) can be calculated using the formula: \[ \text{EAT} = \text{hit ratio} \times (\text{TLB access time}) + (1 - \text{hit ratio}) \times (\text{page table lookup time} + \text{memory access time}) \] Given: - **Hit ratio** = 0.80 - **TLB access time** = 100 nanoseconds - **Main memory access time** = 100 nanoseconds - **Page table lookup time** = 100 nanoseconds (as stated, one memory access) \[ \text{EAT} = 0.80 \times 100 + (1 - 0.80) \times (100 + 100) \] \[ \text{EAT} = 80 + 0.20 \times 200 = 80 + 40 = 120 \text{ nanoseconds} \] Thus, the correct answer is **120 nanoseconds**.