---------------- Some administrivia --------------

Reaching me
    Office Hour Thurs 11:15--12:15 (i.e. after class)
    email gottlieb@nyu.edu
    x8-3344
    715 Broadway room 1001

Midterm & Final & Labs & Homework

    Lab != Homework  Describe both

    Labs can be run on home machine
         ... but you are responsible
         Please PLEASE upload a copy to ACF

Upper Left board for announcements ... but you are responsible.

Handouts are low tech, not great (a feature!)

Web page: http://allan.ultra.nyu.edu/gottlieb/os

Comment on the text

    The "right" text is Tannenbaum's "Distributed OS", but that book
    has a high overlap with the second part of "Modern OS" and you
    already own the latter (V22.202 used it).

----------------  Chapter 9, Intro to Distributed Systems ----------------

Enablers

    Powerful micros: Inexpensive machines worth connecting

    High-speed LANs: Move data quickly

       Low latency: Small transfers in about a ms
       High Bandwidth: 10 Megabits/sec (now 100 "soon" 1000)

    Gave rise to Distributed (as opposed to Centralized) systems

(Somewhat vague) Definition of a distributed

    A distributed system is a collection of independent computers that
    appears to the users of the system as a single computer.          

Advantages over centralized

    Repeal of grosch's law--indeed the reverse occurred (diminishing
    returns) so that now dist sys are more cost efficient

    Absolute performance beyond a single system

        Big web engine

        Weather prediction

    Sometimes the natural soln since the problem is distributed

        Branches of a bank

        Computer supported cooperative work

    Incremental growth

    Reliability

        In principle you have redundancy so fault tolerance

Advantages over independent machines

    Data sharing

    Device sharing

        Sometimes more expensive than the computer

    Communication (between people)--email

    Flexibility

        In addition to the symmetric soln of each user gets
        pc/wkstation can have some more powerful and/or specialized
        machines.

Disadvantages of distributed systems

    Immature software

    Network failure / saturation

    Security

    Reliability

        Often with a dist sys you need ALL the components to work

HOMEWORK 9-1

Hardware configuration and concepts.

    Book shows its age a little here

    Flynn's classification of machines with multiple CPUs

        SISD: Single Instruction stream Single Data stream

        SIMD: Process arrays all at once

        MISD: Perhaps doesn't exist; not important

        MIMD: Each CPU capable of autonomy