Chapter 4 - Terms Flashcards
(39 cards)
aging:
a policy used to ensure that jobs that have been in the system for a long time in
the lower-level queues will eventually complete their execution.
context switching:
the acts of saving a job’s processing information in its PCB so the job can be swapped out of memory and of loading the processing information from the PCB of another job into the appropriate registers so the CPU can process it. Context switching occurs in all preemptive policies.
CPU-bound:
a job that will perform a great deal of nonstop computation before issuing an I/O request. It contrasts with I/O-bound.
earliest deadline first (EDF):
a preemptive process scheduling policy (or algorithm) that
selects processes based on the proximity of their deadlines (appropriate for real-time
environments).
first-come, first-served (FCFS):
a nonpreemptive process scheduling policy (or
algorithm) that handles jobs according to their arrival time.
high-level scheduler:
a synonym for the Job Scheduler.
I/O-bound:
a job that requires a large number of input/output operations, resulting in
substantial free time for the CPU. It contrasts with CPU-bound.
indefinite postponement:
signifies that a job’s execution is delayed indefinitely.
interrupt:
a hardware signal that suspends execution of a program and activates the
execution of a special program known as the interrupt handler.
interrupt handler:
the program that controls what action should be taken by the operating system when a certain sequence of events is interrupted.
Job Scheduler:
the high-level scheduler of the Processor Manager that selects jobs from
a queue of incoming jobs based on each job’s characteristics.
job status:
the state of a job as it moves through the system from the beginning to the
end of its execution.
low-level scheduler:
a synonym for the Process Scheduler.
middle-level scheduler:
a scheduler used by the Processor Manager when the system to remove active processes from memory becomes overloaded. The middle-level scheduler swaps these processes back into memory when the system overload has cleared.
multiple-level queues:
a process scheduling scheme (used with other scheduling algorithms) that groups jobs according to a common characteristic.
multiprogramming:
a technique that allows a single processor to process several programs residing simultaneously in main memory and interleaving their execution by
overlapping I/O requests with CPU requests.
natural wait:
an I/O request from a program in a multiprogramming environment that
would cause a process to wait “naturally” before resuming execution.
nonpreemptive scheduling policy:
a job scheduling strategy that functions without
external interrupts so that once a job captures the processor and begins execution, it remains in the running state uninterrupted until it issues an I/O request or it’s finished.
preemptive scheduling policy:
any process scheduling strategy that, based on predeter-
mined policies, interrupts the processing of a job and transfers the CPU to another job.
It is widely used in time-sharing environments.
priority scheduling:
a nonpreemptive process scheduling policy (or algorithm) that
allows for the execution of high-priority jobs before low-priority jobs.
process:
an instance of execution of a program that is identifiable and controllable by
the operating system.
Process Control Block (PCB): a
a data structure that contains information about the
current status and characteristics of a process.
Process Scheduler:
a low-level scheduler that establishes the order in which processes
in the READY queue will be served by the CPU.
process status:
information stored in the job’s PCB that indicates the current location in memory of the job and the resources responsible for that status.
