With Cook unveiling iOS 8 at the Keynote, WWDC 2014, you are wondering if it would work with your device. Like every major iOS upgrade, iOS 8 will be supported on all devices that support iOS 7 except the oldest one.
Don't Miss This: iOS 8 Features
Here's a handy iOS 8 compatibility chart for you.
iOS 8 Compatible Devices
iPhone: iPhone 5s, 5c, 5, 4s
iPod: iPod touch 5th gen
iPad: iPad 3, iPad Air, iPad 4th-gen and iPad 2
iPad mini: iPad mini (original) and iPad mini 2 (retina display)
As you can note, the device that fell out of favor is iPhone 4. (There might be some minor upgrades to iOS 7.x intermittently but that's about it. Upgrade to a better iPhone if you want to relish the features of iOS 8).
The iPod touch 4th gen is also out of the game.
Obviously, these devices feature older hardware that would not be able to effectively run iOS 8 in all its glory. Apple routinely kicks out older devices out of the compatibility list so that the experience of newer iOS is not tainted by unsupported hardware.