Assignment 6, due Feb. 23
the homework for CS:3620, Spring 2018
On all assignments, your name must be legible as it appears on your University ID card! Assignments are due at the start of class on the day indicated (usually Friday). Exceptions will be by advance arrangement unless there is what lawyers call "an act of God" (something outside your control). Homework must be turned in on paper, either in class or in the teaching assistant's mailbox. Never push late work under someone's door!
In a uniform interleaving, you use every i'th sector where the interval between successive sector numbers is a constant. The interleaving 0-2-4-6-1-3-5-7 is non-uniform because, while i=2 in most cases, the jump from 6 to 1 uses i=3 and the jump from 7 back to 0 uses i=1.
The sequence given by i=1 is usually described as non-interleaved, but technically, it is the simplest uniform interleaving.
a) List all of the uniform interleavings on 8 sectors, and for each, state the value of i. (0.5 points)
b) Give a general rule. If the disk has s sectors per track, what values of i give distinct uniform interleavings. (There is a formally correct mathematical description of the required relationship between s and i.) (0.5 points)
a) Which use of the extra RAM allowed both floppy disks to be used for user data once the system was up and running? (0.3 points)
b) Which use of the extra RAM accelerated access to user files as well as system programs. (0.3 points)
c) Which use of the extra RAM required extra effort when a floppy disk was ejected from its drive? Explain the problem. (0.4 points)
a) Where does the disk scheduler go? Specifically, is there any need for a disk scheduler for the mounted disk image? Briefly, why or why not? (0.5 points)
b) What if the natural block size (the sector size) of my real disk differs from the natural block size of my mounted disk image file. Would this be easier to deal with using the Unix read() and write() kernel calls as a disk interface, or using the linearized sector number scheme outlined in the notes for Feb. 21? Briefly explain your answer. (0.5 points)