How does nginx parallelize requests?

Question

Nginx

If I open two tabs in the same browser with the same script where sleep(10); //secs then the script will work first in one tab, and then in another.
If you open a tab on another computer, the script will complete the work in parallel
How can I explain this?

Answer 1

https://en.wikipedia.org/wiki/Event_loop

Answer 2

nginx has nothing to do with it. It's your browser that notices that the second tab goes to the same address as the one already open and doesn't send the request. hopes that the answer received on the first request can be used in the second too. If you add headers that allow caching, then it will be so.