$4.$a$.$ Discuss the concept of virtual memory and discuss its

implementation.

$4.$b$.$The CPU accesses the following block location in the order shown

below. There are four blocks in cache memory and $8$ blocks in main

memory. Give the cache content configuration at each instant. Also

calculate Hit ratio, if FIFO replacement technique is being employed.

$3,2,5,7,2,4,1,6,7,5,2,1,3,6,2,5,7,4,1,3,7.$ Assume cache was empty at the

beginning.