Concurrency refers to the ability of a system or processor or core to handle multiple tasks at the same time, but not necessarily executing them simultaneously. It's about managing multiple tasks in a way that makes them appear as though they're happening at the same time.
Parallelism is about performing multiple tasks simultaneously. It's the literal simultaneous execution of computations or processes on multiple processors or cores.
Example
- Concurrency: Think of each car as a task or process. Multiple cars can be on the highway at the same time, even if they're not all driving side-by-side. This represents concurrency, where multiple tasks can be in progress, but they might not be executing simultaneously.
- Parallelism: Now, imagine the cars are all driving side-by-side in the different lane. This represents parallelism, where multiple tasks are executing at the same time.
Here are the key points:
- Concurrency: Multiple tasks can be in progress at the same time, but they might not be executing simultaneously.
- Parallelism: Multiple tasks are executing simultaneously.
- Concurrency can exist without parallelism: Multiple cars on a highway can be concurrent without being parallel if they're in different lanes.
- Parallelism always implies concurrency: If multiple tasks are executing simultaneously, they must be concurrent.