convention the contents of memory beyond the current top of the stack are

Convention the contents of memory beyond the current

This preview shows page 50 - 52 out of 84 pages.

Image of page 50
-51- A A NSWERS TO NSWERS TO Q Q UESTIONS UESTIONS 9.1 Long-term scheduling: The decision to add to the pool of processes to be executed. Medium-term scheduling: The decision to add to the number of processes that are partially or fully in main memory. Short-term scheduling: The decision as to which available process will be executed by the processor 9.2 Response time. 9.3 Turnaround time is the total time that a request spends in the system (waiting time plus service time. Response time is the elapsed time between the submission of a request until the response begins to appear as output. 9.4 In UNIX and many other systems, larger priority values represent lower priority processes. Some systems, such as Windows, use the opposite convention: a higher number means a higher priority 9.5 Nonpreemptive: If a process is in the Running state, it continues to execute until (a) it terminates or (b) blocks itself to wait for I/O or to request some operating system service. Preemptive: The currently running process may be interrupted and moved to the Ready state by the operating system. The decision to preempt may be performed when a new process arrives, when an interrupt occurs that places a blocked process in the Ready state, or periodically based on a clock interrupt. 9.6 As each process becomes ready, it joins the ready queue. When the currently- running process ceases to execute, the process that has been in the ready queue the longest is selected for running. 9.7 A clock interrupt is generated at periodic intervals. When the interrupt occurs, the currently running process is placed in the ready queue, and the next ready job is selected on a FCFS basis. 9.8 This is a nonpreemptive policy in which the process with the shortest expected processing time is selected next. 9.9 This is a preemptive version of SPN. In this case, the scheduler always chooses the process that has the shortest expected remaining processing time. When a new process joins the ready queue, it may in fact have a shorter remaining time than the currently running process. Accordingly, the scheduler may preempt whenever a new process becomes ready.
Image of page 51
Image of page 52

You've reached the end of your free preview.

Want to read all 84 pages?

  • Spring '12
  • MICHEAL
  • Operating Systems, Virtual memory, Central processing unit, .........

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture