Question

Hey, I'm hoping that someone can help with this problem I am stuck on.

A personal computer salesman visiting a college in Italy remarked during his sales pitch his company had devoted substantial effort to making their version of UNIX very fast. As an example, he noted their disk driver used the elevator algorithm and also queued multiple requests within a cylinder in sector order. A student, Larry 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 he measured was identical to what would be expected from first-come, first-served. Was the salesman lying?

Answer 1

Answer:


Not necessarily. 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. Harry should have
started up many processes at the same time to see if the elevator algorithm worked.