Unit II Process Management
Process
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.
2
Heap
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.
What are the operations on process?
A process is a program in execution and it is more than a program code called as
text section and this concept works under all the operating system because all the
task perform by the operating system needs a process to perform the task
The process executes when it changes state. The state of a process is defined by
the current activity of the process.
Each process may be any one of the following states −
New − The process is being created.
Running − In this state the instructions are being executed.
Waiting − The process is in waiting state until an event occurs like I/O
operation completion or receiving a signal.
Ready − The process is waiting to be assigned to a processor.
Terminated − The process has finished execution.
Process
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.
2
Heap
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.
What are the operations on process?
A process is a program in execution and it is more than a program code called as
text section and this concept works under all the operating system because all the
task perform by the operating system needs a process to perform the task
The process executes when it changes state. The state of a process is defined by
the current activity of the process.
Each process may be any one of the following states −
New − The process is being created.
Running − In this state the instructions are being executed.
Waiting − The process is in waiting state until an event occurs like I/O
operation completion or receiving a signal.
Ready − The process is waiting to be assigned to a processor.
Terminated − The process has finished execution.
