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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.


a job that will perform a great deal of nonstop processing before issuing an interrupt

first come, first served (FCFS)

a nonpreemptive process scheduling policy/algorithm that handles jobs according to their arrival time


a job that requires a large number of input/output operations, resulting in much free time for the CPU

indefinite postponement

signifies that a job's execution is delayed indefinitely because it is repeatedly preempted so other jobs can be processed


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 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 condition of a job as it moves through th system from the beginning to the end of its execution

middle-level scheduler

a scheduler used by the processor manager to manage processes that have been interrupted because they have exceeded their allocated CPU time slice

multiple-level queues

a process scheduling scheme that groups jobs according to a common characteristic


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

a common term used to identify 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 executions, it remains in the running stat uninterrupted until it issues an I/O request or it's finished

preemptive scheduling policy

any process scheduling strategy that, based on predetermined 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 that allows for th execution of high-priority jobs before low-priority jobs


an instance of execution of a program that is identifiable and controllable by the operating system

Process Control Block (PCB)

a data structure that contains information about the current status and characteristics of a process

Process scheduler

the low-level scheduler of the Processor Manager that establishes the order in which processes in the READY queue will be served by the CPU

Process scheduling algorithm

an algorithm used by the Job Scheduler to allocate the CPU and move jobs through the system

process scheduling policy

any policy used by the Processor Manger to select the order in which incoming jobs will be executed

process status

information stored in the job's PCB that indicates the current position of the job and the resources responsible for that status


(1) a synonym for the CPU, (2) any component in a computing system capable of performing a sequence of activities


an interactive unit, such a file stored on a disk


a linked list of PCBs that indicates the order in which jobs or processes will be serviced

response time

a measure of the efficiency of an interactive system that tracks the speed with which the system will respond to a user's command

round robin

a preemptive process scheduling policy that allocates to each job one unit of processing time per turn to ensure that the CPU is equally shared among all active processes and isn't monopolized by any one job

shortest job next (SJN)

a nonpreemptive process scheduling policy that selects the waiting job with the shortest CPU cycle time

shortest remaining time (SRT)

a preemptive process scheduling policy similar to the SJN algorithm that allocates the processor to the job closest to completion


the basic unit of concurrent programming languages that defines a sequence of instructions that may be executed in parallel with other similar units


a portion of a program that can run independently of other portions. Multithreaded applications programs can have several threads running at one time with the same or different priorities

time quantum

a period of time assigned to a process for execution before it is preempted

turnaround time

a measure of a system's efficiency that tracks the time required to execute a job and return output to the user

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