My iphone app doesn't run well on the iPhone 3G. Can I make it so users with these models can't download the app? If so, what does a 3G user see when they search for my app in the app store?
Does it appear in the store at all for them? If it does, when are they notified that they can't download the app?
Make it run better. Or if it's not completely unusable, just let them use it anyway. People with old devices expect them to be a bit slow.
According to the iTunes Connect Developer Guide (which links to the iOS Application Programming Guide), you can't prohibit certain devices. You can, however, require certain features which are only present on new devices:
armv7 is what I'd recommend (older devices are armv6)magnetometer, because older devices don't have one. Apple might look at you funny if your app doesn't actually use the compass though.opengles-2, because older devices only support 1.1. Apple might look at you funny too.auto-focus-camera, except the iPad and all the iPod Touches don't have one. Probably not what you want.I recommend you use the UIRequiredDeviceCapabilities key in your info.plist. This lets you tell the App Store exactly which capabilities you require instead of which device you require. If your app "doesn't run well" on a 3G I'll guess it is because of performance and therefore you'd want to require a newer processor. Look into setting arm7 as one of your required device capabilities. For more info look here: http://developer.apple.com/iphone/library/documentation/General/Reference/InfoPlistKeyReference/Articles/iPhoneOSKeys.html#//apple_ref/doc/uid/TP40009252-SW3