iOS (iPhone/iPod Touch) Fetch Vs. Push

Question

Going through advanced Mail, Contacts, Calendars settings on my iPod Touch with iOS 4.0, I noticed an option for fetch, instead of push. What exactly is the difference between fetch and push for the user, and how much does it affect my battery life?

I'm assuming it's for alerts that come from an application but not from a server, and the fetch setting time is the amount of time they are allowed to push out these messages or something? I think I'm wrong, I'm confused.

Answer 1

Push is a triggered event that uses less power.* A kind of "invisible SMS" message is sent to the phone when there is e-mail, and the phone then checks your e-mail.

Fetch is a timed operation, using more power, because it will check every X minutes to see if there is mail (even if there is no new mail) and will continue to check at intervals.

*Push can use more power, but only in the case where you get new mail more than your fetch interval. Ex: If you get new mail every 5 minutes all day, you'll check e-mail 3 times in 15 minutes on push. Fetch would check it once every 15 minutes (configurable). If you get a TON of e-mail, you might need to stay on Fetch.

Answer 2

As Sathya said in their comment; fetch is periodic checks every X minutes / manually and push data to the device. The reason for choice being given is that push can be taxing to the battery and if you're not fussed about getting alerts instantly you might opt for fetch.