LAST UPDATED ON: SEPTEMBER 16, 2024
Process in Operating System
A process in operating system is a program in execution which then forms the basis of all computation. The process is not as same as program code but a lot more than it. A process is an 'active' entity as opposed to the program which is considered to be a 'passive' entity. Attributes held by the process include hardware state, memory, CPU, etc.
Process memory is divided into four sections for efficient working :
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The Text section is made up of the compiled program code, read in from non-volatile storage when the program is launched.
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The Data section is made up of the global and static variables, allocated and initialized prior to executing the main.
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The Heap is used for the dynamic memory allocation and is managed via calls to new, delete, malloc, free, etc.
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The Stack is used for local variables. Space on the stack is reserved for local variables when they are declared.
![process in OS]()
The different Process States
Processes in the operating system can be in any of the following states:
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NEW- The process is being created.
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READY- The process is waiting to be assigned to a processor.
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RUNNING- Instructions are being executed.
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WAITING- The process is waiting for some event to occur(such as an I/O completion or reception of a signal).
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TERMINATED- The process has finished execution.
![process states]()
Process Control Block
There is a Process Control Block for each process, enclosing all the information about the process. It is also known as the task control block. It is a data structure, which contains the following:
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Process State: It can be running, waiting, etc.
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Process ID and the parent process ID.
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CPU registers and Program Counter. Program Counter holds the address of the next instruction to be executed for that process.
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CPU Scheduling information: Such as priority information and pointers to scheduling queues.
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Memory Management information: For example, page tables or segment tables.
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Accounting information: The User and kernel CPU time consumed, account numbers, limits, etc.
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I/O Status information: Devices allocated, open file tables, etc.
![process control block]()
OS Process vs a Program
Let us take a look at the differences between Operating system Process and a Program:
| OS Process |
Program |
| The process is basically an instance of the computer program that is being executed. |
A Program is basically a collection of instructions that mainly performs a specific task when executed by the computer. |
| A process has a shorter lifetime. |
A Program has a longer lifetime. |
| A Process requires resources such as memory, CPU, Input-Output devices. |
A Program is stored by hard-disk and does not require any resources. |
| A process has a dynamic instance of code and data |
A Program has static code and static data. |
| Basically, a process is the running instance of the code. |
On the other hand, the program is the executable code. |
When there are two or more runnable processes then it is decided by the Operating system which one to run first then it is referred to as Process Scheduling.
A scheduler is used to make decisions by using some scheduling algorithm.
Given below are the properties of a Good Scheduling Algorithm:
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Response time should be minimum for the users.
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The number of jobs processed per hour should be maximum i.e Good scheduling algorithm should give maximum throughput.
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The utilization of the CPU should be 100%.
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Each process should get a fair share of the CPU.
![process scheduling]()
