Comp111 - Quiz 2 Review Answers

Dec 8, 2009 - closed book



Please fill in the blanks. Each blank is worth 5 points.

  1. There are three important statistical distributions important in modelling operating systems. The ____exponential____ distribution models inter-arrival times for events. Its cumulative distribution function is ____y=1-e(-λx)____ The ____exponential____ distribution models service times for individual processing requests. These distributions are both ____memoryless____, e.g., service times for ____prior/past____ requests do not affect the service time for the next request.
  2. In Kendall notation, an M/M/infinity queue is one in which arrival times are ____poisson____, service times are ____exponential____, and there are an infinite number of ____servers____.
  3. Suppose we have an M/M/1 queue with arrival factor λ and service factor μ. This queue has a stable behavior if ____λ/μ____<1, but ____saturates/overfills/etc____ when ____λ/μ____>=1. (both blank 9's have same answer). In the latter case, the queue length _______increases____ without bound.
  4. A monitor differs from a semaphore in two ways:
    1. It does not ____buffer/queue____ signals; uncaught signals are ____ignored/dropped____.
    2. It is bound (via a programming language) to a specific ____data structure____. It is not possible to erroniously utilize a monitor to access a different one.
  5. A(n) ____interrupt____ tells the operating system that attention is needed for a device or peripheral; a(n) ____signal____ tells a process that attention is needed. The operating system cannot receive a(n) ____signal____ any more than a process can handle a(n) ____interrupt____
  6. Process memory is naturally divided into ____segments____ that contain ____pages____, each of which contains a fixed number of bytes. A typical byte of memory can be divided into three bit fields including a(n) ____segment____ address, ____page____ address, and word address.
  7. Inverted page tables provide a(n) ____more____ efficient mechanism for memory mapping than ____hierarchical____ page tables, because the number of pages kept in memory is often far less than the total number of virtual pages available.