Tutorial Week 10

Questions

Q1: What is thrashing? How can it be detected? What can be done to combat it?

Q2: A disk has an average seek time of 5ms, a rotational speed of 15,000 rpm, and 500 sectors per track. What is the average access time to read a single sector? What is the expected time to read 500 contiguous sectors on the same track? What is the expected time to read 500 sectors scattered over the disk?

Q3: Describe programmed I/O and interrupt-driven I/O in the case of receiving input (e.g. from a serial port). Which technique normally leads to more efficient use of the CPU? Describe a scenario where the alternative technique is more efficient.

Q4: A device driver routine (e.g. read_block() from disk) is invoked by the file system code. The data for the filesystem is requested from the disk, but is not yet available. What do device drivers generally do in this scenario?

Q5: Describe how I/O buffering can be formulated as a bounded-buffer producer-consumer problem.

Q6: An example operating system runs its interrupt handlers on the kernel stack of the currently running application. What restriction does this place on the interrupt handler code? Why is the restriction required?