Question

Calculate the effective access time for a system with 80% tlb hit ratio, 15 ns for searching tlb, 100 ns main memory access time

Answer 1

TLB is called hit ratio.

An 80 percent hit ratio ,for example hit ratio hit ratio,for example means that we find the desired page number in the TLB 80 percent of the time.

If it takes 100 nanoseconds to acess memory to acess memory then a mapped memory acess takes 100 nanoseconds when the page number is in the TLB.

If we fail to find the page in the TLB then we must first acess the page table and for the frame number.

(100 nanoseconds) and then acess the desired byte in memory (100 nanosecods) and then acess the desired byte in memory (100 nanoseconds) for a total of 200 nanoseconds.

To find the effective memory acess time, we weight the case by its probability:effective acess time = 0.80*100+0.20*200=120nanosecods.