I've recently installed XCode 6.0.1 complete version and it came with default iOS 8 simulators. My current project is targeted to iOS 6, so I did copy old iOS simulators into new XCode (as I did it before with old versions of XCodes). But in the simulators' list I can't distinguish the appropriate iOS version. I don't know which of them iOS 6 or iOS 8.
Below paths are where I copied old simulators from and into respectively
/Applications/Xcode 5.1.1.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs
/Applications/Xcode 6.0.1.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs
Wow... why did you do that? The only simulators supported by Xcode 6 are the ones for iOS 7.0, 7.1 & 8.0.
Delete your simulators and go to Xcode > Preferences > Downloads and download all the available simulators.
Afterwards your simulators list should look like this:
CoreSimulator only supports iOS 7.0 and newer.
Xcode's run destinations will try to disambiguate devices with the same name by using "(OS Version)". If there are two devices with the same name and OS version, it will use the device's UDID (the long string you are seeing) to disambiguate. You can clean up your devices (remove duplicates) using the simctl command line argument (run: xcrun simctl help) or the device manager in Xcode.app.
来源：https://stackoverflow.com/questions/25994272/select-an-appropriate-ios-version-from-simulators-list-in-xcode-6-0-1