CS439: Principles of Computer Systems
(Source: Alison Norman.)
Due: 11:59 PM Monday, April 1, 2013 Homeworks
will be submitted electronically. Please refer to
the homework turnin instructions.
Sam P. Hacker is a Head Guru in a software company known for
operating systems with very sorry quality. Hacker suggested a trick to
reduce the pressure on the swap space. Instead of swapping out pages
that belong to code texts into the swap area, the operating system
could just take away the memory frames. If the code page is needed
later, it could be paged directly from its binary file. Hacker's
argument is that the operating system will save time by not storing
the code page into the swap space, and will save space in the swap
area. The code text exists on disk anyway, and could be fetched from
there. Would you approve of this design? Why or why not?
Disk requests come into the disk driver for tracks 10, 22, 20, 2, 40,
6, and 38, in that order. A seek takes 6 msec per track moved. How
much seek time is needed for the following scheduling
c) LOOK (SCAN, but doesn't
move to the end)
In all cases, the arm is initially at track
20. (Note that SCAN is a synonym for the elevator algorithm.)
Adapted from Tannenbaum Chapter 5 Number 24.
Suppose I have a disk such as the 320GB SATA drive
described here and I have a workload
consisting of 10,000 reads to sectors randomly scattered across the
disk. How long in expectation will these 10,000 request take (total) assuming the
disk services requests in FIFO order?
The MegaGiga hard disk rotates at 5400 rpm with an arm seek time given
by = 4 + 0.05t msec, where t is the number of tracks the
arm seeks. Assume a sector size of 1024 bytes, and 2048 tracks with 512
The disk controller and DMA read or write data from/to disk at a rate of
What is the storage capacity of the disk?