Process Management

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 State

Process Statues Register

Registers

Event Information

Memory Management Information

Resource Held

I/O status

File Management Information

Accounting Information

                                                            Process Control Block

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