Process management deals with the assignment of
processor to different tasks being performed by the computer system. The
processor management module of the operating system consists of three
components: job scheduler, which
deals with the management of jobs, process
scheduler, which deals with the management of processor, Traffic Controller¸ which keeps track of the status of the
processes.
A job is a sequence of job steps, each job step
being the execution of a program. For example, a job involving the compilation
and execution of a program written in a high level language involves the
following steps:
·
Execution of the compiler to compile the user’s program
·
Execution of the linker and loader to prepare and load executable pro
gram
·
Execution of the user’s program
A process or a task is a program in execution. A process
is the smallest unit of work individually scheduled by an operating system. The
concepts of program and process are different. Process is a dynamic concept
undergoing frequent state and attribute changes. While an executable program is
a static process template that may rise to one or more processes.
A process is created by an operating system in
response to a user command. When a new
process is created, the operating system performs the following actions:
·
Create a Process Control Block of the process,
·
Allocate memory and other resources to the process
·
Sets up the process environment and
·
Initialize resource accounting information for the process.
Process
Control Block
The operating system groups all the information that
it needs about a particular process into a data structure called Process
Control Block (PCB) or Process Descriptor. Whenever a process is created, the
operating system creates a corresponding PCB to serve its run-time description
during the life time of the process. When the process terminates, its PCB
removed. The figure illustrates fields in a PCB.
PCB Pointer
|
Process Id
|
Priority
|
Process Statues Register
|
Registers
|
Event Information
|
Memory Management
Information
|
Resource Held
|
I/O status
|
File Management
Information
|
Accounting Information
|
Process Control Block
NEXT: Process States
Previous: Multiprocessor Operating System
Index : Operating System
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