Multitasking,Multi programming & Multiprocessing

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Multitasking (Time sharing)

Multitasking has the same meaning of multiprogramming but in a more general sense, as it refers to having multiple (programs, processes, tasks, threads) running at the same time. 

This term is used in modern operating systems when multiple tasks share a common processing resource (e.g., CPU and Memory).

Multitasking:As the name itself suggests, multi tasking refers to execution of multiple tasks (say processes, programs, threads etc.) at a time. 

Ex: In the modern operating systems, we are able to play MP3 music, edit documents in Microsoft Word, surf the Google Chrome all simultaneously, this is accomplished by means of multi tasking.

Multitasking is a logical extension of multi programming.

Multi programming 

In a modern computing system, there are usually several concurrent application processes which want to execute. 

Now it is the responsibility of the Operating System to manage all the processes effectively and efficiently.

One of the most important aspects of an Operating System is to multi program.

In a computer system, there are multiple processes waiting to be executed, 

i.e. they are waiting when the CPU will be allocated to them and they begin their execution. These processes are also known as jobs. 

Now the main memory is too small to accommodate all of these processes or jobs into it. 

Thus, these processes are initially kept in an area called job pool. This job pool consists of all those processes awaiting allocation of main memory and CPU.

CPU selects one job out of all these waiting jobs, brings it from the job pool to main memory and starts executing it.

The processor executes one job until it is interrupted by some external factor or it goes for an I/O task.

Multiprocessing 

In a uni-processor system, only one process executes at a time.

Multiprocessing is the use of two or more CPUs (processors) within a single Computer system. 

The term also refers to the ability of a system to support more than one processor within a single computer system. 

Now since there are multiple processors available, multiple processes can be executed at a time. 

These multi processors share the computer bus, sometimes the clock, memory and peripheral devices also

Within the past several years, multiprocessor systems (also known as parallel systems or multicore systems)

The multiple-processor systems in use today are of two types. Some systems use asymmetric multiprocessing, in which each processor is assigned a specific task.

A boss processor controls the system; the other processors either look to the boss for instruction or have predefined tasks. This scheme defines a boss–worker relationship.

The most common systems use symmetric multiprocessing (SMP), in which each processor performs all tasks within the operating system.

A recent trend in CPU design is to include multiple computing cores on a single chip. Such multiprocessor systems are termed multicore.