Parallelism vs. Concurrency

Parallelism

Parallel

adj. beside one another 2

In our case, parallel in time. Opposite of sequential or serial:

  ^ Task
  |
1 +    +---------------+
  |
2 +    +-----------------------+
  |
  +--------------------------------------->
                                       Time

Concurrency

Concurrent

adj. in competition

In our case, over resources:

  ^ Task
  |
1 +         +----*          +----*
  |
2 +   +----*      +----*
  |
  +--------------------------------------->
                                       Time

The Trick

The trick in remembering which is which, is that parallelism has the usual english meaning 2. But semantics of concurrency in this context are of french origin 1.

Unfortunately, in english these words are synonyms. The french meaning seems absent from english language. Which makes things a bit confusing.