4. (i) Write policies are needed for data caches when an instruction writes data to the cache. Briefly describe the Write Back and Write Through policies. (5 marks) (ii) Comment on the following statement giving reasons. "Hit ratio can be improved by using faster memory, i.e. memory with less access time." (5 marks) (iii) A disk subsystem employed for the virtual memory organization has the following specifications: 32 sectors per track, 512 bytes per sector, 3600 rpm, average linear latency of 30 ms, page size of 4 Kbytes. In average the computer system executes an instruction in 1.5us. I. Calculate the data transfer rate of the disk subsystem. II. Compute the wasted time in the event of a page fault while executing a program. What should be the seek time of the disk drive in order to reduce the wasted time, to less than 85%? (10 marks)