1998 Problem Set
Problem 1 (20 points)
You have become involved with a project to build an "Information
Mural", a wall-sized computer screen for displaying
information. The users of the device would like to save all
their active windows on the display and restore them sometime in
the future when they return to the display. The model would be
like closing a laptop and opening it back up later and picking
up where you left off. Unlike a laptop, other users would take
over the mural between the save and restore.
Arbitrary application programs running on a computer
that drives the mural generate the windows. The computer is
running a modern operating system such as Unix or Windows NT. As
an OS person, you are asked how difficult it would be to enhance
an operating system so that it would be possible to support this
new mode of usage. Describe what changes would need to be made
to the operating system. What would the problem areas and
limitations of the approach be?
Problem 2 (12 points)
While early work on synchronization such as monitors are still
in wide use today, researchers are becoming interested in
non-blocking synchronization. Describe the advantages and
disadvantage of non-blocking synchronization as compared to
monitors. When would you choose one over the other for a design?
Problem 3 (14 points)
There has been a long debate in the operating system community
as to the role of transactions in operating systems. One school
of thought is that transactions should be first class OS
citizens with the operating system providing high-level
interface (begin, commit, abort) and all system services
operating under transactions. The other school of thought is
that operating systems provide support for building
transactional systems but shouldn't implement the transactions.
Describe the arguments for and against each of these
viewpoints.
Problem 4 (14 points)
For each of the security related problems below, describe how
encryption technology (public and shared key algorithms, message
digests, etc.) can help deal with the problem.
a) Recently we have had problems in Gates with hackers
running network snoop programs that watch rlogin and telnet
streams for passwords being typed. Assuming we aren't going to
give up on password-based authentication, explain how it is
possible to log into a remote system without having the password
exposed on the wire to these snoop programs.
b)Trojan Horse attacks like leaving a program that
looks like a login screen running on a machine at Sweet Hall
have long been an annoyance. Describe how encryption technology
can defeat this kind of an attack.