Process Management
A process is basically a program in execution. The execution of a process must progress in a
sequential fashion.
A process is defined as an entity which represents the basic unit of work to be implemented
in the system.
To put it in simple terms, we write our computer programs in a text file and when we
execute this program, it becomes a process which performs all the tasks mentioned in the
program.
When a program is loaded into the memory and it becomes a process, it can be divided into
four sections ─ stack, heap, text and data. The following image shows a simplified layout of
a process inside main memory −
S.N. Component & Description
1 Stack
The process Stack contains the temporary data such as method/function
parameters, return address and local variables.This is dynamically allocated memory to a process during its run time.
3 Text
This includes the current activity represented by the value of Program
Counter and the contents of the processor's registers.
4 Data
This section contains the global and static variables.
Program
A program is a piece of code which may be a single line or millions of lines. A computer
program is usually written by a computer programmer in a programming language. For
example, here is a simple program written in C programming language −
#include <stdio.h>
int main() {
printf("Hello, World! \n");
return 0;
}
A computer program is a collection of instructions that performs a specific task when
executed by a computer. When we compare a program with a process, we can conclude that
a process is a dynamic instance of a computer program.
A part of a computer program that performs a well-defined task is known as an algorithm.
A collection of computer programs, libraries and related data are referred to as a software.
Process Life Cycle
When a process executes, it passes through different states. These stages may differ in
different operating systems, and the names of these states are also not standardized.
In general, a process can have one of the following five states at a time.
S.N. State & Description
1 Start
This is the initial state when a process is first started/created.
2 Ready
The process is waiting to be assigned to a processor. Ready processes are waiting
to have the processor allocated to them by the operating system so that they can
run. Process may come into this state after Start state or while running it by but
interrupted by the scheduler to assign CPU to some other process.
3 Running
Once the process has been assigned to a processor by the OS scheduler, the
process state is set to running and the processor executes its instructions.
4 Waiting
Process moves into the waiting state if it needs to wait for a resource, such as
waiting for user input, or waiting for a file to become available.
5 Terminated or Exit
Once the process finishes its execution, or it is terminated by the operating system,
it is moved to the terminated state where it waits to be removed from main
memory.
Process Control Block (PCB)
A Process Control Block is a data structure maintained by the Operating
System for every process. The PCB is identified by an integer process ID
(PID). A PCB keeps all the information needed to keep track of a process
as listed below in the table −
S.N. Information & Description
1 Process State
The current state of the process i.e., whether it is ready, running, waiting,
or whatever.
2 Process privileges
This is required to allow/disallow access to system resources.
3 Process ID
Unique identification for each of the process in the operating system.
4 Pointer
A pointer to parent process.
5 Program Counter
Program Counter is a pointer to the address of the next instruction to be
executed for this process.
6 CPU registers
Various CPU registers where process need to be stored for execution for
running state.
7 CPU Scheduling Information
Process priority and other scheduling information which is required to
schedule the process.
8 Memory management information
This includes the information of page table, memory limits, Segment table
A process is basically a program in execution. The execution of a process must progress in a
sequential fashion.
A process is defined as an entity which represents the basic unit of work to be implemented
in the system.
To put it in simple terms, we write our computer programs in a text file and when we
execute this program, it becomes a process which performs all the tasks mentioned in the
program.
When a program is loaded into the memory and it becomes a process, it can be divided into
four sections ─ stack, heap, text and data. The following image shows a simplified layout of
a process inside main memory −
S.N. Component & Description
1 Stack
The process Stack contains the temporary data such as method/function
parameters, return address and local variables.This is dynamically allocated memory to a process during its run time.
3 Text
This includes the current activity represented by the value of Program
Counter and the contents of the processor's registers.
4 Data
This section contains the global and static variables.
Program
A program is a piece of code which may be a single line or millions of lines. A computer
program is usually written by a computer programmer in a programming language. For
example, here is a simple program written in C programming language −
#include <stdio.h>
int main() {
printf("Hello, World! \n");
return 0;
}
A computer program is a collection of instructions that performs a specific task when
executed by a computer. When we compare a program with a process, we can conclude that
a process is a dynamic instance of a computer program.
A part of a computer program that performs a well-defined task is known as an algorithm.
A collection of computer programs, libraries and related data are referred to as a software.
Process Life Cycle
When a process executes, it passes through different states. These stages may differ in
different operating systems, and the names of these states are also not standardized.
In general, a process can have one of the following five states at a time.
S.N. State & Description
1 Start
This is the initial state when a process is first started/created.
2 Ready
The process is waiting to be assigned to a processor. Ready processes are waiting
to have the processor allocated to them by the operating system so that they can
run. Process may come into this state after Start state or while running it by but
interrupted by the scheduler to assign CPU to some other process.
3 Running
Once the process has been assigned to a processor by the OS scheduler, the
process state is set to running and the processor executes its instructions.
4 Waiting
Process moves into the waiting state if it needs to wait for a resource, such as
waiting for user input, or waiting for a file to become available.
5 Terminated or Exit
Once the process finishes its execution, or it is terminated by the operating system,
it is moved to the terminated state where it waits to be removed from main
memory.
Process Control Block (PCB)
A Process Control Block is a data structure maintained by the Operating
System for every process. The PCB is identified by an integer process ID
(PID). A PCB keeps all the information needed to keep track of a process
as listed below in the table −
S.N. Information & Description
1 Process State
The current state of the process i.e., whether it is ready, running, waiting,
or whatever.
2 Process privileges
This is required to allow/disallow access to system resources.
3 Process ID
Unique identification for each of the process in the operating system.
4 Pointer
A pointer to parent process.
5 Program Counter
Program Counter is a pointer to the address of the next instruction to be
executed for this process.
6 CPU registers
Various CPU registers where process need to be stored for execution for
running state.
7 CPU Scheduling Information
Process priority and other scheduling information which is required to
schedule the process.
8 Memory management information
This includes the information of page table, memory limits, Segment table
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