Concurrency vs Parallelism

Concurrency (Multithreading on a Single Processor)

Concurrency means executing multiple tasks at the same time but not necessarily simultaneously. When you have to perform more than one task but you have a single resource then we go for concurrency. In a single-core environment, concurrency is achieved by context switching. (the execution of multiple tasks is interleaved, instead of each task being executed sequentially one after another.)

For example: This is a bit like chatting with different people through various IM windows; although you’re actually switching back and forth, the net result is that you’re having multiple conversations at the same time.

Parallelism (Multithreading on multi-core) (Multiprocessing)

Parallelism means that your program leverages the hardware of multi-core machines to execute tasks at the same time by breaking up work into tasks, each of which is executed on a separate core.

Example

For example: In a browser, multiple tabs can be different threads. MS Word uses multiple threads: one thread to format the text, another thread to process inputs

Note

Concurrency & parallelism are concepts

Multithreading are implementations