Chapter 4 - Terms

Question 1

aging:

Answer 1

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.

Question 2

context switching:

Answer 2

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.

Question 3

CPU-bound:

Answer 3

a job that will perform a great deal of nonstop computation before issuing an I/O request. It contrasts with I/O-bound.

Question 4

earliest deadline first (EDF):

Answer 4

a preemptive process scheduling policy (or algorithm) that
selects processes based on the proximity of their deadlines (appropriate for real-time
environments).

Question 5

first-come, first-served (FCFS):

Answer 5

a nonpreemptive process scheduling policy (or

algorithm) that handles jobs according to their arrival time.

Question 6

high-level scheduler:

Answer 6

a synonym for the Job Scheduler.

Question 7

I/O-bound:

Answer 7

a job that requires a large number of input/output operations, resulting in
substantial free time for the CPU. It contrasts with CPU-bound.

Question 8

indefinite postponement:

Answer 8

signifies that a job’s execution is delayed indefinitely.

Question 9

interrupt:

Answer 9

a hardware signal that suspends execution of a program and activates the
execution of a special program known as the interrupt handler.

Question 10

interrupt handler:

Answer 10

the program that controls what action should be taken by the operating system when a certain sequence of events is interrupted.

Question 11

Job Scheduler:

Answer 11

the high-level scheduler of the Processor Manager that selects jobs from
a queue of incoming jobs based on each job’s characteristics.

Question 12

job status:

Answer 12

the state of a job as it moves through the system from the beginning to the
end of its execution.

Question 13

low-level scheduler:

Answer 13

a synonym for the Process Scheduler.

Question 14

middle-level scheduler:

Answer 14

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.

Question 15

multiple-level queues:

Answer 15

a process scheduling scheme (used with other scheduling algorithms) that groups jobs according to a common characteristic.

Question 16

multiprogramming:

Answer 16

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.

Question 17

natural wait:

Answer 17

an I/O request from a program in a multiprogramming environment that
would cause a process to wait “naturally” before resuming execution.

Question 18

nonpreemptive scheduling policy:

Answer 18

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.

Question 19

preemptive scheduling policy:

Answer 19

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.

Question 20

priority scheduling:

Answer 20

a nonpreemptive process scheduling policy (or algorithm) that
allows for the execution of high-priority jobs before low-priority jobs.

Question 21

process:

Answer 21

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

Question 22

Process Control Block (PCB): a

Answer 22

a data structure that contains information about the

current status and characteristics of a process.

Question 23

Process Scheduler:

Answer 23

a low-level scheduler that establishes the order in which processes
in the READY queue will be served by the CPU.

Question 24

process status:

Answer 24

information stored in the job’s PCB that indicates the current location in memory of the job and the resources responsible for that status.

Question 25

processor:

Answer 25

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

Question 26

program:

Answer 26

a unit of instructions.

Question 27

queue:

Answer 27

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

Question 28

response time:

Answer 28

one measure of the efficiency of an interactive system that tracks the
time required for the system to respond to a user’s command.

Question 29

Round Robin:

Answer 29

a preemptive process scheduling policy (or algorithm) 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.

Question 30

scheduling algorithm:

Answer 30

an algorithm used by the Job or Process Scheduler to allocate the CPU and move jobs or processes through the system.

Question 31

scheduling policy:

Answer 31

any policy used by the Processor Manager to select the order in which incoming jobs, processes, and threads will be executed.

Question 32

shortest job next (SJN):

Answer 32

a nonpreemptive process scheduling policy (or algorithm) that selects the waiting job with the shortest CPU cycle time.

Question 33

shortest remaining time (SRT):

Answer 33

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

Question 34

task:

Answer 34

(1) the term used to describe a process, or (2) the basic unit of concurrent programming languages that defines a sequence of instructions that may be executed in parallel with other similar units.

Question 35

thread:

Answer 35

a portion of a process that can run independently.

Question 36

Multithreaded systems

Answer 36

can have several threads running at one time with the same or different priorities.

Question 37

Thread Control Block (TCB):

Answer 37

a data structure that contains information about the

current status and characteristics of a thread.

Question 38

thread status:

Answer 38

information stored in the thread control block that indicates the current
position of the thread and the resources responsible for that status.

Question 39

time quantum:

Answer 39

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