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At this time of year one often finds high stress levels among
graduate students here at Madison, since we're enjoying the
screening exams process.  Students who want to pursue doctoral
degrees must pass a set of difficult exams in computer science
within a certain time period.  We must pass one depth (four
hour) exam, and two breadth (two hour) exams in different
subject areas.

One of my friends came up with a great way to apply his
nervous energy (and cynical wit), which was to write this
wonderful parody of an Operating Systems screening exam.

Some of the humor is particularly poignant to people familiar
with the particular exam, since the questions are recognizable
twists on topics that seem to always come up.  For example,
Question 1 is about the paper "On the Duality of Operating
System Structures" by Lauer and Needham, [Proc. 2nd Int'l
Symposium on Operating Systems, IRIA, October 1978].  And
Question 8 is clearly about the controversy over whether
network file servers should be stateless or maintain state.

Even without this "inside" knowledge, this exam is very funny.
My friend is shy about posting this himself, but I think it
deserves a wide audience, so I twisted his arm until he agreed
to let me submit it.




                      Computational Pedantry


Instructions:

For the BREATH exam: Answer any 4 of questions 1-6.

For the DEATH exam: Answer any 6 of questions 1-6, and any 5 of
questions 7-10.  You are expected to spend about two hours on each
fifth of the exam.  You are allowed to spend about two hours on
each half of the exam.


BREATH QUESTIONS

Breath 1.  Duolity:

In principle, Batman/Robin and Electrawoman/Dynagirl superheros
should have similar power and performance.  In practice, most
Batman/Robin TV programs have achieved better popularity than
Electrawoman/Dynagirl programs.

(2a) Describe two opportunities for tasteful dress or believable
     plot offered by a typical Batman/Robin program that are not
     offered by a typical Electrawoman/Dynagirl program.  Explain
     why these optimizations occur more often in the Batman/Robin
     programs.

(2b) Describe how advertising buffers between episodes may be
     implemented in a Batman/Robin program with strictly premium
     channels.


Breath 3.  Resource Management:

Every resource management system needs protection against overuse
or abuse of the resource.  Three general strategies are preven-
tion, avoidance, and detection & recovery.

(3a) Describe these strategies, carefully distinguishing between
     them, and give an example of each.

(3b) Give specific arguments for and against applying the detec-
     tion & recovery strategy mentioned in N. Wirth's paper "Pro-
     gram Development Through Stepwise Refinement."


Breath 5.  Encryption:

Pbafvqre n flfgrz jurer vagrecebprff pbzzhavpngvba vf ivn
zrffntrf.  Nyy zrffntr pbzzhavpngvba orgjrra znpuvarf vf
rapelcgrq.  Gur rapelcgvba shapgvba pna or cynprq ng nal bs
frireny yriryf va gur flfgrz.  Qrfpevor gur nqinagntrf naq qvfnqi-
nagntrf bs rnpu bs gurfr nygreangvirf.

(5a) Rnpu xreary vf erfcbafvoyr sbe rfgnoyvfuvat n frpher punaary
     gb rnpu bgure xreary gb juvpu vg gnyxf.

(5b) Rnpu cebprff vf erfcbafvoyr sbe rfgnoyvfuvat n frpher punaary
     gb rnpu bgure cebprff gb juvpu vg gnyxf.

(5c) Gur argjbex freivpr cebivqref (tngrjnlf, ebhgref, rgp.) ner
     erfcbafvoyr sbe rfgnoyvfuvat frpher punaaryf.



DEATH QUESTIONS


Death 8.  Tasteless/Tasteful Hosts:

A so-called tasteless host is  one  that  does  not  maintain  any
information  about  guests  between  parties.   For this question,
assume parties are not replicated (no party is held in  more  than
one veranda).

(8a) How would you accomplish catering with a tasteless server?

(8b) How does recovery from guests trashing the lawn at  a  taste-
     less  host  party  differ from recovery at a party that main-
     tains open invitations?

(8c) Consider a tasteless server where you  have  multiple  guests
     wanting to speak simultaneously to a given host.  How can you
     enforce consistency of access such that all  eats  and  bytes
     from  the server appear to obey some serialization?  What are
     the performance ramifications of providing such consistency?


Death 9.  Synchronization:

(9a) Briefly describe the  principal  differences  between  "doing
     lunch" and "you MUST call me" primitives.

(9b) Describe problems which arise when  distance  vector  routing
     algorithms are used and how these may or may not be corrected
     by "doing lunch."

(9c) How have the presence of hall monitors  affected  development
     of these primitives?


Death 10.  Distributed Shared Memory:

A single virtual address space  can  be  supported  simultaneously
across  the  (homogeneous)  processors of a collection of worksta-
tions distributed across a local area network.

(10a)
     Implement such a scheme.

(10b)
     Integrate your scheme into the following three  kernels,  and
     give performance estimates on the modified systems:

	(1)  UNIX

	(2)  OS/360

	(3)  THE

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