Operating Systems Design
                             1996-97 Fall
                            Allan Gottlieb

                    Text: Silbershatz and Galvin

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


All registered students are entitled to a sun acct (wwh 405)

Reaching me
    Office Hours TT 4-5 
    email gottlieb@nyu.edu
    x8-3344
    715 bway room 1001

Midterm & Final & Labs & HW
    Lab != HW  Describe both
    Labs can be run on home machine ... but you are responsible

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

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

-------------   End of Administrivia ----------------

Layers of abstraction used to hide details

    Applications and Utilities
    Libraries
    OS proper (kernel)
    Hardware

    All but applications are sys software.  Sometimes
    called operating system

OS raised the level of abstraction and hides details like devices from
its users.

OS, i.e. kernel, is itself layered

    Device (machine) independent
    device drivers machine specific code.

    Some kernels are more extensively layered with some
    abstractions implemented in terms of others.

             Filesystem may be on top of other abstractions.

The OS is a resourse mgr (so users don't conflict)

The OS is a control program (similar)

OS goals:  Convenience to user; efficiency.

How is OS different from say compilers?

    Concurrency !

    "The main difficulty of multiprogramming is that concurrent
    activities can interact in a time-dependent manner, which
    makes it practically impossible to locate programming errors
    by systematic testing.  Perhaps, more than anyything else,
    this explains the difficulty of making operating systems
    reliable"  Per Brinch Hansen, *Operating Systems Principles*
    1973

    Show failure.  Interrupt handler puts request on list.  Main
    line OS code removes.  #items++  #items--

Homework: Fix the above failure

History (VERY brief)

    Single User (No OS)
        Mention bendix G15  and IBM 1620 experiences
        paper tape, cards, delete key, scotch tape, etc

    Batch:  Uniprogrammed, run-to-completion
        Resident monitor
        Online devices

    "Concurrent" I/O:
        Pipelined parallelism  
        Offline pre- and post-processing (tapes)
        Spooling (disk)

    Multiprogramming
        Overlap CPU and I/O of a single job
        Multiple batches
        CPU Scheduling (which ready job to run
        MFT vs MVT
            Latter potentially more efficient but
            brings in serious mem mgt questions.

    Time sharing
    
        PREEMPTIVE job scheduling
        Often use (on-) demand paging (aka virt mem, but not
        by me) 

    PCs and workstations

        Commodity OS
        Strong push for distributed systems and networked
        systems

    Multiprocessor OS
        Master Slave
        Symmetric

    Distributed systems

        Resource sharing

        Communication

        Speedup (not so clear)

        Reliability (not so clear)

             a distributed system is one in which a
             computer I've never seen can stop me from
             getting my work done--loosely quoted from
             somewhere

    Real-time systems

        Soft vs hard -- In the latter missing a deadline is
        fatal, perhaps literally

Homework: 1.1 1.3 1.5 1.8 1.11 "why are dist sys not desirable?"

End of Ch 1.

==================== End of Lecture 1 ===========================