Concurrency vs parallelism

The two terms are commonly used interchangeably, and most times it seems as they can be.

But they have two different definitions, and when you talk about supporting concurrency or supporting parallelism you’re talking about two distinct tasks.


The capability of interchanging multiple different tasks.

Such as when you’re shopping you can at any time swap between looking for apples or looking for bread. A shoppinglist is inheritly a concurrent list of tasks.

Allowing concurrency means you allow switching tasks at any point.


Doing multiple things at the same time, simontaneously. This depends on the fact that the tasks support concurrency.

Such as when you’re shopping with friends. You can give each friend a section of the shopping list, and all items on the list will be retrieved in parallel.

Allowing parallelism means you allow multiple tasks to be worked on simontaneously.