Currently, there are four known possible choices: The first letter in the model number represents the source of the device. Depending on the software displaying the string, there may be a slash (' /') followed by a character. Afterwards is either one or two characters representing the ' region' of the device's origin. This is followed by four characters between either 'A' and 'Z' or '0' and '9' (most commonly only digits). The model number of a device begins with a variable first letter representing the source of the device (replacement, engraved, etc. The model number of your device is located in the Settings app on the 'General -> About' screen under 'Model'. This page is used to give an overview of the different model numbers (or 'M' numbers) used by devices. IOS runs on various different models of devices.
