If it is to be after list iPhone compatible, published by Apple for iOS 11, we'll see that the recommended minimum so we can install and run the new operating system, it is iPhone 5s. If iPad, it is recommended not to be older than iPad Air, while for iPod, the only one that supports iOS 11 is iPod 6th generation touch.
What you need to know, however, is that this list of compatible devices iOS 11 does not guarantee good functioning of the devices. If iPhone 5S si iPhone 6, there are many users who complain that iPhoneCPC It's going very hard after install iOS 11. Very difficult to answer ordersis blocking in applications or even it remains stuck and it becomes nonfunctional.
Apple we have become accustomed in recent years to the launch of a major version of iOS to coincide with the launch date of a iPhone. The launch events take place around mid-September.
iOS 11 has been launched with iPhone 8, iPhone 8 Plus si iPhone X in 2017, iOS 10 came with iPhone 7 si iPhone 7 Plus in 2016, iOS 9 cu iPhone 6S si iPhone 6S Plus in 2015 and so on.
Even if a new version of iOS appears in the list of compatible devices and some 3-4 years old, our recommendation is not to install this new version, except on a device with a maximum of two generations ago. In the case of iOS 11, it is not recommended to install it on iPhone 5S or iPhone 6. The processors of these devices will hardly face the new iOS.
Although iPhone SE is the last penultimate in the list iPhone Compatible with iOS 11, this model was launched in the spring of 2016, being a "special edition" that has more powerful features and hardware support than iPhone 6 and iPhone 6 Plus. Basically, under his case iPhone SE we find the same processor as at iPhone 6S si iPhone 6S Plus. So, you can run iOS 11 smoothly on iPhone SE.
If you managed to upgrade to iOS 11 on a iPhone older, and it works very hard, the problem is downgradeto the previous version. The transition from iOS 11 la iOS 10.3.3.
You can do this using the application iTunes and file IPSW which contains the iOS 10.3.3 compatible operating system for your model iPhone or iPad. Download IPSW is available on the official website of Apple.
Downgrade from iOS to iOS 11 10.3.3 can't do for iPhone 8, iPhone 8 Plus si iPhone X. The minimum system supported by these devices is iOS 11.