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73 lines
3.5 KiB
Plaintext
73 lines
3.5 KiB
Plaintext
DRAFT
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TO: Area II Committee
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DATE: April 22, 1975
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RE: Oral Qualifying Examination for Mr. Dave Reed
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An oral examination of Mr. Reed was held on Friday April 18,
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by a committee consisting of Professors Mitter, Schroeder and Hewitt
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(chairman). Mr. Reed spent about forty five minutes discussing his
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thesis work, and after a recess spent over an hour answering questions
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and solving problems on the blackboard. Dave performed exceedingly
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well on the problems and his masters thesis research is first rate.
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On the basis of all the evidence the committee felt that Mr. Reed
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should be p_a_s_s_e_d_ and be q_u_a_l_i_f_i_e_d_ at this time in the doctoral program.
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Dave's thesis concerns simplifying and generalizing the
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implementation of processes in MULTICS. Currently processes in
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MULTICS provide many useful services for the user but they are
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expensive to create and maintain. Dave has taken the approach of
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building a small fixed number of virtual processors as a base on which
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to build the general MULTICS processes. The capabilities of virtual
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processors are closely matched to the capabilities of the actual
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physical processors of the machine. Two very important design goals
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of his thesis are to simplify and increase the security of MULTICS.
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Professor Mitter asked how Dave could be sure that the security of
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MULTICS had in fact been increased by these measures. Professor
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Hewitt asked Dave to describe similarities and differences of his
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virtual processors and the virtual machines as implemented on the
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IBM-370. Professor Mitter asked Dave about the possibilities for
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formally modeling his implementation with Petri Nets. Dave had tried
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this but found the restriction of not being able to add new places or
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transitions to a Petri to be a crucial deficiency in the model. This
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limitation restricts Petri Nets to finite state control.
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Professor Schroeder then asked Dave to describe the techniques
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of contiguous allocation and block allocation memory schemes. Dave
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answered the question succinctly pointing out the relative advantages and
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disadvantages of each scheme. Professor Schroeder then asked Dave to
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give a rough calculation of the wasted space for each scheme. Dave
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did the calculation assuring a uniform distribution of block sizes.
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Professor Schroeder then pointed out that a uniform distribution was
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not a realistic assumption.
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Professor Hewitt asked Dave to implement LISP lists in the lambda-
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calculus. Dave proceeded to do this by giving lambda-expressions for
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CONS, CAR, CDR. He was asked whether his definitions would run if
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translated into LISP. Dave answered that it depended on the version
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of LISP and explained two common schemes for implementing LISP.
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Professor Hewitt then asked if he could translate his definitions of CONS
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into an ALGOL-like language with procedures as values. Dave easily did this
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and explained how the usual implementation of ALGOL would have to be changed.
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Dave was then asked to add operations RPLACA and RPLACD to his definition of
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CONS. He did this and explained how the change further affected the
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implementation of the language.
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Professor Mitter asked Dave to formally define the notion of a
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finite state machine. Dave was a little rusty on his automata theory
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but was able to come up with the defintion. He was then asked to
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define the reduced machine after some thrashing around he hit upon the
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idea of a homorphism.
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Sincerely,
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Carl E. Hewitt
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CEH/yw |