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State two advantages and two disadvantages of a layered operating system.

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CCM 3070Y:\svn\trunk\engine\docs\working\acumen3\85822.doc

Coursework 1

Question 1

State two advantages and two disadvantages of a layered operating system.


-  Advantages of layered operating systems are:

  1. It is decomposable and therefore effects separation of concerns and different abstraction levels
  2. It allows good maintenance, where you can make changes without affecting layer interfaces

- Disadvantages of layered operating systems are:

  1. It is difficult to exactly assign of functionalities to the correct and appropriate layer
  2. Because of having too many layers, performance of the system is


Question 2

a. Give definitions for: turnaround time, throughput, processor utilisation

b. When might a context switch occur? What exactly is saved? Why?

c. In the presence of asynchronous interrupts, even the most innocent

    looking program can produce mysterious results. If concurrency can

    produce subtle bugs, why use it?


a. Turnaround time: - is the time taken between the submission and complete

                                 execution of a process, which includes the actual running      

                                 time and waiting time for accessing the resources


...read more.


b. A context switch occurs when a thread releases the processor, and whereby

    the task/process of the front of the ready queue becomes the new active

    task. The execution context of the previous thread has to be saved so that

    the thread can be used later. Mainly, the program counter and the

    execution stack associated with the executing thread is saved, so that the

    context of a new thread can be restored.

c. We use concurrency because it allows multiple users to share a machine and

    programming is made easier by breaking a problem into simple pieces.

    Moreover, concurrency also provides other advantages such as timesharing,

    parallel processing, overlapping computation with Input/Output and solution

    for larger problems.

Question 3

List the responsibilities in UNIX of:        a. the shell        b. the kernel


a. Responsibilities of the shell in UNIX:

        - to provide a command line interface (CLI)

        - to perform Input/Output redirection

        - to perform pathname substitution

        - to perform parameter/variable substitution

...read more.


Question 6

A computer systems uses segmentation and paging. When a segment is in memory, some words are wasted on the last page. A segment of size s will have s/p pages of size p. How do the page table size and the last page wastage each vary with page size? Find by calculation or otherwise the page size which will give the least overhead.


Bibliography & References


J. S. Swift, “Virtual Machinges II”, ©2002, School of Computing Science

Silberschatz, A., Galvin, P.B., and Gagne, G., Applied Operating Systems, Concepts, 1st Edition, J.Wiley and Sons, 2001

Tanenbaum, A. S., Modern Operating Systems, 2nd Edition, Prentice Hall, 2001





Gasthurie Kanagachandran                 2035883

...read more.

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