Operating systems, just part b please a.) A personal computer salesman visiting

Question

Operating systems, just part b please a.) A personal computer salesman visiting a university remarked during his sales pitch that his company had devoted substantial effort to making their version of UNIX very fast. As an example, he noted that their disk driver used the elevator algorithm and also queued multiple requests within a cylinder in sector order. A student, Harry Hacker, was impressed and bought one. He took it home and wrote a program to randomly read 10,000 blocks spread across the disk. To his amazement, the performance that he measured was identical to what would be expected from first-come, first-served. Was the salesman lying? b.) turnin this part: Describe the test that Harry Hacker should have run to properly test the disk system

Explanation / Answer

a) No the Salesman was not necessirily lying as reads are synchronous. That is, there is no prefetching and there was a single thread requesting disk blocks.

In other words, there was only a single request in the queue at any time.

A UNIX program that reads 10,000 blocks issues the requests one at a time, blocking after each one is issued until after it is completed. Thus the disk driver sees only one request at a time; it has no opportunity to do anything but process them in the order of arrival.

b)  Harry should have started up many processes at the same time to see if the elevator algorithm worked.

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