Definition
Concurrent processing means that more than one task is in progress at the same time: one task starts before another has finished. On a single core each task is given a slice of processor time in turn, which gives the appearance of the tasks running simultaneously. With more than one core, different tasks can be executed by different cores at the same instant.
Concurrent vs Parallel Processing
Key Point
| Feature | Concurrent processing | Parallel processing |
|---|---|---|
| Hardware basis | One core is enough, shared by time-slicing; several cores can be used as well | Needs more than one core or processor |
| Execution style | Tasks overlap in time; on one core the processor switches rapidly between them | Tasks are executed at the same instant |
| Simultaneity | Apparent on one core, real across several | Real |
| Typical benefit | Responsiveness with limited hardware | Higher throughput for independent workloads |
Worked Example
Worked Example: Multitasking Computer
Tasks: browser, music player, software update.
Result (concurrent): each task progresses via rapid switching.
Result (parallel): tasks run truly simultaneously on different cores. This is still concurrent processing: running tasks in parallel is one way of achieving it.
Tasks: browser, music player, software update.
| Time slice (single core) | Browser | Music | Update |
|---|---|---|---|
| 1 | Running | Waiting | Waiting |
| 2 | Waiting | Running | Waiting |
| 3 | Waiting | Waiting | Running |
| 4 | Running | Waiting | Waiting |
| Core (multi-core) | Assigned task |
|---|---|
| Core 1 | Browser |
| Core 2 | Music player |
| Core 3 | Software update |