I updated my 4S from IOS 5.0.1 to IOS 5.1 via iPhone itself. I remember the file is only around 189MB and update success. Today, I played around with iTunes with my iPhone connected. When I click "Restore" - iTunes was going to update the iPhone with the latest software even though iTunes knew that the iPhone already had 5.1 installed. Now iTunes is downloading the update (5.1) - and I notice that the file being downloaded is 803.0MB. My question is about file size: 189MB vs 803.0MB. Is there anything different? With that huge gap, I assume there must be something different? Is it like Full Installation vs Upgrade? Is it better to have clean installation (full install) instead of upgrade? It shouldn't make any different. In Windows OS, it's better to have full clean installation instead of upgrade. Can someone verify? And which one is better?