Homework 1

CS 502

Due:  February 9

  1. What is the purpose of system calls, and how do system calls relate to the Operating System and to the concept of dual-mode operation?  Discuss system calls from the perspectives of the OS as a resource manager and as a provider of virtual computers.
  2. In virtually all systems that include DMA modules, DMA access to main memory is given higher priority than processor access to main memory.  Why?
  3. Our discussion of process states and the corresponding event queues maintained by the operating system suggests that a process can only be in one event queue at a time.
    1. Is it possible that you would want to allow a process to wait on more than one event at the same time? Provide an example.
    2. In that case, how would you modify the queueing structure to support this new feature?
  4. Most Round-robin schedulers use a fixed-sized quantum.  Give an argument in favor of a small quantum.  Now give an argument in favor of a large quantum.  Compare and contrast the types of systems and jobs to which the arguments apply.  Are there any for which both are reasonable?
  5. Consider the following set of processes, with the given arrival time, CPU burst time, and priority:

Process

Arrival Time Burst Time Priority
A 0 15 6
B 5 9 3
C 8 3 7
D 3 6 9
E 10 12 4
      1. Draw four Gantt charts illustrating the execution of these processes using FCFS, SJF, a non-preemptive priority (a smaller priority number implies a higher priority), and Round Robin with time quantum = 1.
      2. What is the turnaround time of each process for each schedule?
      3. What is the waiting time of each process for each schedule?
  1. Which type of process is generally favored by a multilevel feedback queuing scheduler -- a processor-bound process or an I/O bound process?   Explain why.