Question

A computer keeps its page tables in memory. The overhead required for reading a value from memory is 3 microseconds. The computer has a TLB, which holds pairs of virtual pages and physical page frames: .

a) What is the effective access time if the TLB has an access time of 500 ns, and we observe a 20% TLB miss rate?
b) What is the effective access time if the TLB has an access time of 900 ns, and we observe a 95% hit rate?

Answer 1

To calculate the effective access time, consider both the TLB access time and the TLB miss rate. The effective access time is the sum of the TLB access time and the time it takes to read a value from memory.

Step-by-step explanation:

a) To calculate the effective access time, we need to consider both the TLB access time and the TLB miss rate. First, we calculate the time it takes to access the TLB: 500 ns x 0.2 (20% miss rate) = 100 ns. Then, we calculate the time it takes to read a value from memory: 3 microseconds. Finally, we add these two times together to get the effective access time: 100 ns + 3 microseconds = 3.1 microseconds.

b) In this case, the TLB hit rate is 95%, so we calculate the time it takes to access the TLB: 900 ns x 0.95 (95% hit rate) = 855 ns. Again, we add the time it takes to read a value from memory: 3 microseconds. The effective access time is therefore: 855 ns + 3 microseconds = 3.855 microseconds.