• A program consists of instructions in any programming language.
• A process consists of instructions in machine code. A program in execution is called a process.
• Thread is the basic unit of execution or CPU utilization. 

Scope

This article discusses programs, processes, and threads. It also explains different types of processes.

Definition

A program is a passive entity, which is a file containing a list of instructions stored on a disk (often called an executable file). A process on the other hand is an active entity with a program counter specifying the next instruction to be executed and a set of associated resources. A program becomes a process when an executable file is loaded into memory.

Difference between program and process

PROGRAM	PROCESS
It consists of instructions in any programming language.	It consists of instructions in machine code.
It resides in the secondary storage device	It resides in the main memory
The program only needs memory for storage	The resource requirement is quite high in the case of process
Its life span is unlimited.	Its life span is limited
It is a passive entity.	It is an active entity.

A process includes a stack, data section, and heap. Stack contains temporary data such as function parameters, return address, and local variables. The data section contains global variables. Heap is a memory that is dynamically allocated during process runtime.

A thread is a basic unit of CPU utilization. It comprises a shared ID, a program counter, a register set, and a stack. It shares code section, data section, and other operating system resources such as open files and signals.

Difference between process and thread

THREAD	PROCESS
Threads are easier to create and terminate	Processes are not easy to create and terminate.
Multiple threads when they are in the same process share the same address	Processes do not share the same address
It is easy to communicate between the threads	To communicate between processes we need operating system intervention.
It takes less time in context switching.	It takes more time to context switch.
Thread is lightweight. Each thread in the process shares code, data, and resources.	The process is called a heavyweight process.

Types of processes: 

There are basically two types of event-specific processes

• I/O bound process: If a program/process spends more of its time doing I/O than it spends doing computations then it is called I/O bound process.
• CPU bound process: If a program/process spends more of its time doing CPU operations (computations) and generates I/O requests infrequently then it is called CPU bound process.

Summary

• The program consists of a list of instructions that gets stored on a hard disk.
• When the program goes to RAM and starts running it becomes a process.
• A thread is the smallest unit of execution managed by an operating system.
• There are two types of processes: I/O bound process and CPU bound process.

Special thanks to Avaneet Kaur Saluja for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article