what is threading concept?

First understand that the difference between a process and a thread. There is one and only one process for each exe file. See my An Introduction to Virtual Memory in Windows for an explanation of processes. Threads exist (do work) for a process. A thread's memory is it's process's memory.

Threads existed in Windows even when it was 16-bits and ran under DOS and used processes that did not support virtual memory. 16-bit Windows did not have preemptive (pre-emptive) multitasking but it did have multitasking. Preemptive multitasking means that the operating system can interrupt a program while the program is doing something. Threads have existed in operating systems for over half a century, although many operating systems call them something else; the most common other term is "task". Threads have been used extensively in systems with a single core/processor.

Although threads are usually described as providing concurrency, their original main purpose is to provide asynchronicity. Asynchronicity means that something can happen at any time and the computer needs to deal with something that happens unexpectedly. A common asynchronous event is IO, such as disk IO. When a program copies a file from one disk drive to a different drive, the program can execute twice as fast if it does the IO asynchronously. There would very little advantage to asynchronous IO if the file is copied from and to the same physical drive. Another example of an asynchronous event is windows; more specifically, people. If a program with a UI (graphical or textual as in a console) needs to do some processing independent of the UI, then usually a thread is used for the other (background) processing. Another example of an asynchronous event is inter-system communication (communication between systems); tasks are useful even for intra-system communication (communication between processes).

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