O'Reilly OSCON Java 2011: Martin Odersky, "Working Hard to Keep It Simple" - YouTube:
Concurrency vs Parallelism - What is the difference? - Stack Overflow
Concurrency is when two tasks can start, run, and complete in overlapping time periods. It doesn't necessarily mean they'll ever both be running at the same instant. Eg. multitasking on a single-core machine.
Parallelism is when tasks literally run at the same time, eg. on a multicore processor.
- Parallelism: A condition that arises when at least two threads are executing simultaneously.
- Concurrency: A condition that exists when at least two threads are making progress. A more generalized form of parallelism that can include time-slicing as a form of virtual parallelism.