Download Test 1 Operating Systems and Networking CS

Test 1
Operating Systems and Networking
CS-330
Spring 2009
Answer any five questions from below
Time: 2:00 – 3:50 PM February 23, 2009, in class
Modality: Open book, open note, but no laptop or mobile phone.
1.
2.
3.
One of our lecture note slides on Computer Systems Overview declares: “[Operating System]
provides a set of services to system users.” Who are these system users that OS attempts to
provide service to? What type of “system services” do we anticipate that users must procure
through OS?
On the same slide, it is maintained that an “[Operating System] manages secondary memory and
I/O devices.” Is this a sufficient claim for a start as far as memory is concerned? Elaborate your
answer. If processes within a system communicated via message passing without using shared
memory, would we still insist on it? State your reason.
Consider the following diagram that purports to depict a mouse that could be moved around and
the monitor screen that displays it as a cursor motion. What happens when the mouse begins to be
moved? How does the system realize these specific set of events via the system module A? What
role should A play in this setup if one of the things it must do is to get the CPU first for whatever
it wants to do.
Bus
Application
Programs
Video
Controller
Screen
Device
Drivers
A
Mouse
Controller
Mouse
4.
In one slide on Operating Systems Overview (in fact, the very first slide), an attempt is made to
identify the role of an Operating System as an object. Two points are identified in it: (a) A
program that controls the execution of application programs, and, (b) what acts as an interface
between applications and hardware. Do we need to expand it a little? If so, how? If not, why not?
Are there situations when an OS is not needed? Are there situations when it is mostly OS (and not
much application)?
5.
It is claimed that driving system resources in an “efficient manner” is one major goal of an OS.
Explain the adjective “efficient” in this context. Is there a possibility that it might counter other
objectives we tend to identify an OS with? Elaborate your answer.
6.
What is kernel? What goes into the kernel? Suppose, you have a Mac machine (running Mac OS
on an Intel), and you install under it Windows OS like XP or Vista. What flavor of OS will be
found in the kernel? Rationalize your answer. Could there be some compelling reason to expand
the volume of the kernel instead of keeping it to an absolute minimum? Explain your answer.
7.
Memory protection is an important task for an operating system. Who or what could be the entities
memory needs to be protected from? Couldn’t the task of protecting the memory be left to users
instead of burdening OS? Rationalize your answer. Should this concept be extended to secondary
memory as well when user opens up a file for read/write?
8.
In a time-sharing system, a process might be temporarily deprived of CPU. Indicate those cases in
which such possibilities might result. What must OS require of CPU to do to facilitate a smooth
transition for the target process? What happens to the process if the departure is necessitated by an
(a) I/O call, or, by a (b) system error?
9.
Consider CPU scheduling with 5 jobs in its ready queue, though, not all arriving at the same time.
Each job is indicated by a job ID, by arrival time into the system, and by the total CPU time it
needs. Jobs are:
(A, 3, 7), (B, 4, 3), (C, 5, 3), (D, 6, 4), (E, 6, 2)
Compute the average turn-around and the average queuing times under two disciplines:
a.
b.
SJF (Shortest Job First)
SRTN (Shortest remaining time next)
What conclusions do you derive in this case?