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Learn the core differences between multitasking and multithreading in operating systems. Understand how processes and threads work, how the OS schedules them, and why thread context switching is faster than process context switching. Ideal for CS students and OS beginners!

Introduction

Modern operating systems are designed to handle multiple tasks at once to ensure smooth and efficient execution. This capability is primarily achieved through multitasking and multithreading. While both aim to maximize CPU utilization and responsiveness, they differ in how they handle memory, resources, and execution flow.

Let’s explore the concepts of programs, processes, and threads, followed by a clear comparison between multitasking and multithreading.

Key Concepts

Program

A program is an executable file containing a set of instructions written to perform a specific job or operation.
It is compiled and stored on disk, ready to be loaded into memory for execution.

Process

A process is a program in execution.
It resides in the primary memory (RAM) of the computer.
The OS allocates separate memory and resources to each process for isolation and protection.

Thread

A thread is a lightweight unit of execution within a process.
It represents a single sequence stream within a process.
Multiple threads can run concurrently in a single process, sharing the same memory and resources.
Threads enable parallelism within a program.

Example: In a text editor, typing, spell-checking, and auto-saving might be handled by different threads of the same process.

Multitasking vs Multithreading

Aspect	Multitasking	Multithreading
Definition	Executing more than one task/process simultaneously.	Executing multiple threads of the same process concurrently.
Execution Unit	Multiple processes.	Multiple threads within a single process.
Context Switching	Involves switching between processes.	Involves switching between threads.
CPU Requirement	Works with a single CPU, but performs better with multiple CPUs.	Works best with multiple CPUs or cores.
Memory Usage	Each process has its own memory and resources.	Threads share memory and resources of their parent process.
Isolation	Processes are isolated from each other.	Threads are not isolated, they share memory.
Overhead	Higher due to separate memory allocation.	Lower, as threads use shared memory.

Thread Scheduling

Threads are scheduled based on priority. Even though threads share the same runtime environment, the OS assigns CPU time slices to each thread. This ensures that all threads get a chance to execute, simulating parallelism.

Context Switching: Process vs Thread

Switching Type	Thread Context Switching	Process Context Switching
What is saved?	Thread's state (program counter, registers, stack).	Entire process state, including memory address space.
Speed	Fast	Relatively slow
CPU Cache	Preserved	Flushed

Conclusion

Both multitasking and multithreading are essential techniques used by operating systems to manage tasks and optimize CPU usage. Understanding their differences helps in writing better, more efficient, and scalable programs, especially in multi-core environments.

Whether you’re preparing for interviews or strengthening your OS fundamentals, mastering these concepts is a must.

Unit 3: Multitasking vs Multithreading in Operating Systems: Key Differences

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