It is sometimes said that tape is a sequential-access medium, whereasa magnetic disk is

Chapter 10, Problem 10.7

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It is sometimes said that tape is a sequential-access medium, whereasa magnetic disk is a random-access medium. In fact, the suitabilityof a storage device for random access depends on the transfer size.The term streaming transfer rate denotes the rate for a data transferthat is underway, excluding the effect of access latency. In contrast,the effective transfer rate is the ratio of total bytes per total seconds,including overhead time such as access latency.Suppose we have a computer with the following characteristics: thelevel-2 cache has an access latency of 8 nanoseconds and a streamingtransfer rate of 800 megabytes per second, the main memory has anaccess latency of 60 nanoseconds and a streaming transfer rate of 80megabytes per second, the magnetic disk has an access latency of 15milliseconds and a streaming transfer rate of 5 megabytes per second,and a tape drive has an access latency of 60 seconds and a streamingtransfer rate of 2 megabytes per second.a. Random access causes the effective transfer rate of a device todecrease, because no data are transferred during the access time.For the disk described, what is the effective transfer rate if anaverage access is followed by a streaming transfer of (1) 512 bytes,(2) 8 kilobytes, (3) 1 megabyte, and (4) 16 megabytes?b. The utilization of a device is the ratio of effective transfer rate tostreaming transfer rate. Calculate the utilization of the disk drivefor each of the four transfer sizes given in part a.c. Suppose that a utilization of 25 percent (or higher) is consideredacceptable. Using the performance figures given, compute thesmallest transfer size for disk that gives acceptable utilization.d. Complete the following sentence: A disk is a random-accessdevice for transfers larger than bytes and is a sequentialaccessdevice for smaller transfers.e. Compute the minimum transfer sizes that give acceptable utilizationfor cache, memory, and tape.f. When is a tape a random-access device, and when is it asequential-access device?