1. Why main-memory disk hierarchy is called virtual memory? What are the two motivations behind the development of virtual memory schemes and which one is still relevant? (2 Marks) b. With the help of a diagram for the three level hierarchy of translation lookaside buffer (TLB), in main memory as well as on secondary storage, explain how a virtual dirty bits. (5 Marks) a. Discuss how it is possible to achieve the benefit of large low cost and high speed memory with page tables, and pages memory system works bringing out the significance of the validity, reference, and 2