What is the difference between concurrency and parallelism?

Question

What is the difference between concurrency and parallelism?

Examples are appreciated.

Answer 1

Concurrent programming execution has 2 types : non-parallel concurrent programming and parallel concurrent programming (also known as parallelism).

The key difference is that to the human eye, threads in non-parallel concurrency appear to run at the same time but in reality they don't. In non - parallel concurrency threads rapidly switch and take turns to use the processor through time-slicing. While in parallelism there are multiple processors available so, multiple threads can run on different processors at the same time.

Reference: Introduction to Concurrency in Programming Languages