Multiprogramming, multitasking, multithreading, and multiprocessing are all techniques used in operating systems to make better use of the CPU. Although they are related, they differ in how they handle multiple programs or tasks.
Multiprogramming
Multiprogramming allows multiple programs to reside in the memory at the same time. In a multiprogramming system, the operating system simply switches to and executes another job when the current job needs to wait. The processor is shared among multiple programs, and each program is given a slice of time to execute. Multiprogramming allows multiple users to access system resources simultaneously.
Multitasking
Multitasking allows a single program to execute multiple tasks simultaneously on a CPU machine. These multiple tasks share common resources like CPU and memory. In multitasking systems, the CPU executes multiple jobs by switching among them typically using a small time quantum, and the switches occur so quickly that the users feel like they are interacting with each executing task at the same time.
Multithreading
Multithreading is an extension of multitasking. It allows a single program to execute multiple threads simultaneously on a CPU machine. Each thread has its own path of execution, but they share common resources like CPU and memory. Multithreading can improve the performance of an application by allowing it to perform multiple tasks at the same time.
Multiprocessing
Multiprocessing involves the use of more than one processing unit by a single computer. In multiprocessing, multiple processing units are used by a single device. This technique can improve the performance of an application by allowing it to perform multiple tasks in parallel. Multiprocessing occurs by means of parallel processing.
In summary, the main difference between multiprogramming, multitasking, multithreading, and multiprocessing is that multiprogramming allows multiple programs to reside in the memory at the same time, multitasking allows a single program to execute multiple tasks simultaneously on a CPU machine, multithreading allows a single program to execute multiple threads simultaneously on a CPU machine, and multiprocessing involves the use of more than one processing unit by a single computer.