99% of Developers Don't Get Concurrency

Concurrency and parallelism are fundamentally different concepts that developers often confuse. Concurrency involves handling multiple tasks through interleaved execution on a single CPU core using time slicing or voluntary yielding, making it ideal for IO-bound workloads. Parallelism means truly simultaneous execution across multiple CPU cores or processors, better suited for CPU-bound tasks. The key distinction lies in scheduling approaches: preemptive scheduling where the OS forcibly switches tasks, versus cooperative scheduling where tasks voluntarily yield control. Context switching costs vary significantly between traditional threading (expensive kernel transitions) and modern coroutine-based systems like async/await (lightweight user-space switches).