In operating systems, how are multitasking, multiprogramming and multithreading defined, and how do they differ from each other in the way they share the CPU and system resources?

Introduction / Context:
In modern operating systems it is very common to see many applications and activities appearing to run at the same time. Terms like multitasking, multiprogramming and multithreading describe different techniques that the operating system uses to share the CPU and other resources. This question checks whether you can clearly distinguish these three related but different ideas and connect them to how real systems manage processes and threads.

Given Data / Assumptions:

• We are talking about general purpose operating systems running on a single CPU or a small number of CPUs.

• The operating system supports processes and may also support multiple threads inside a single process.

• The user wants to understand how work is divided between programs, processes and threads.

• Multitasking, multiprogramming and multithreading are treated as related concepts used to improve CPU utilization and responsiveness.

Concept / Approach:
Multitasking is the broad idea that an operating system can run more than one program at the same time from the user point of view. Multiprogramming is an older term that focuses on keeping multiple programs in memory so that the CPU does not sit idle when one program waits for input or output. Multithreading is a more fine grained concept in which a single process contains several threads of execution that share the same code and data but can run independently. The correct option must describe all three ideas in a balanced and technically accurate way and must mention CPU sharing and resource sharing in a clear manner.

Step-by-Step Solution:
Step 1: Think about multitasking. In a multitasking system the operating system rapidly switches the CPU among active processes so that users feel that programs run at the same time. Step 2: Think about multiprogramming. In multiprogramming the operating system keeps multiple programs loaded in memory and selects another ready program when the current program waits for input or output to increase CPU utilization. Step 3: Think about multithreading. In multithreading a single process contains several threads that share memory and resources but each thread has its own program counter and stack and can be scheduled independently. Step 4: Compare each option with these definitions and find the one that correctly combines all three descriptions without mixing them up or stating that they are identical.

Verification / Alternative check:
A quick check is to ask whether the option clearly distinguishes process level concurrency from thread level concurrency. Only one option clearly says that multitasking deals with several programs, multiprogramming focuses on multiple programs in memory to improve CPU usage and multithreading deals with multiple threads in a single process. Also check that the option does not confuse multitasking with multiple CPUs or confuse multiprogramming with storage features. If the option matches the textbook style definitions used in standard operating system books, it is very likely to be correct.

Why Other Options Are Wrong:
Option B is wrong because it claims that multitasking means a single program on many CPUs and that multiprogramming runs only one job at a time, which is the opposite of the real meaning. Option C is wrong because it connects multitasking to many CPUs and says multiprogramming is only about disk storage, which is misleading. It also incorrectly says multithreading is only for graphical applications. Option D is wrong because multitasking, multiprogramming and multithreading are not three names for the same feature; they refer to different levels of concurrency and resource management.

Common Pitfalls:
A frequent mistake is to think that any form of concurrency must involve multiple CPUs, while multitasking and multiprogramming can be implemented on a single CPU using time sharing. Another common confusion is mixing up processes and threads and assuming that multithreading always means separate memory regions, when in fact threads in the same process share most of their memory. Some learners also use the words multitasking and multiprogramming as if they were identical, ignoring their historical context. Being precise about which unit is being scheduled, a process or a thread, helps to avoid these misunderstandings.

Final Answer:
The correct description is: Multitasking lets the CPU rapidly switch among several active programs, multiprogramming keeps multiple programs in memory to improve CPU use and multithreading allows multiple threads of a single process to execute concurrently.