Question: Review the system with one CPU and four drives below:
• CPU W = 4 ms (the average time to execute 1,000 instructions)
• Drive A = 45 ms (average data access speed)
• Drive B = 3 ms (average data access speed)
• Drive C = 17 ms (average data access speed)
• Drive D = 10 ms (average data access speed)
Calculate I/O access speed using this CPU and each of the four disk drives as they evaluate the following track requests in this order: 0, 31, 20, 15, 20, 31, 15. Then, in each case, calculate the access speeds after the track requests are reordered and rank the four disk drives before and after reordering.