How parallel workers finish the same jobs sooner

Synthetic English narration.

The same eight jobs
Here are eight independent jobs. Each block keeps the same duration throughout. One worker must finish them in sequence. These are illustrative work units, not measured seconds.

Open more lanes
With four workers, several jobs run at once. When a worker finishes, it takes the next waiting job. No individual job becomes faster.

Overlap shortens the wait
Watch the same clock on both schedules. The parallel run finishes in seven units instead of twenty-four. Overlapping independent work shortens the time until everything is done.

The last job still matters
Near the end, some workers are idle while others finish. This uneven tail prevents perfect scaling. More workers cannot split a job that must stay together.

Some work cannot overlap
Now include setup and the final join. Those serial steps remain. Total time becomes twenty-seven units versus ten. Parallel work helps, but serial work limits the gain.