Concurrency versus parallelism

Concurrency and parallelism are often mistaken for the same thing, but there is a distinction between them. Concurrency is the ability to run multiple things at the same time, not necessarily in parallel. Parallelism is the ability to do a number of things at the same time.

Imagine you take your other half to the theater. There are two lines: that is, for VIP and regular tickets. There is only one functionary checking tickets and so, in order to avoid blocking either of the two queues, they check one ticket from the VIP line, then one from the regular line. Over time, both queues are processed. This is an example of concurrency.

Now imagine that another functionary joins, so now we have one functionary per queue. This way, both queues will be processed each by its own functionary. This is an example of parallelism.

Modern laptop processors feature multiple cores (normally two to four). A core is an independent processing unit that belongs to a processor. Having...