How many $$32K\,\, \times \,\,1RAM$$ chips are needed to provide a memory capacity of $$256$$ $$K$$-bytes?

Consider the virtual page reference string $$$1,2,3,2,4,1,3,2,4,1$$$
On a demand paged virtual memory system running on a computer system that has main memory size of $$3$$ page frames which are initially empty. Let $$LRU,$$ $$FIFO$$ and $$OPTIMAL$$ denote the number of page faults under the corresponding page replacement policy. Then

A multilevel page table is preferred in comparison to a single level page table for translating virtual address to physical address because.

Consider a disk system with $$100$$ cylinders. The requests to access the cylinders occur in following sequence:
$$4, 34, 10, 7, 19, 73, 2, 15, 6, 20$$
Assuming that the head is currently at cylinder $$50,$$ what is the time taken to satisfy all requests if it takes $$1$$ $$ms$$ to move from one cylinder to adjacent one and shortest seek time first policy is used?