Here’s How iOS Push Notifications Work

There’s a short article on Medium where the author explains how iOS push notifications work. Apple added push notifications in 2009.
Push notifications were introduced to the greater public by Apple in 2009 to solve the problem of wanting to receive messages in real time without having to run the entire app in the background. Until then, there were two predominant methods of sending notifications to applications.
There aren’t a lot of technical details but that makes it easier for people to understand.