What does the model number refer to? There are two different "model numbers" for Apple products.

For example, the Apple TV 4K has:


MQD22LL/A
A1842


Which is the "model number" and what is the other number called?
A… is a model number, referring to the model of device.
M… is a part number, referring to a specific configuration of a model.

For example, for devices with various configurations such as whether a device is unlocked and international, the model number will be identical to a US device but the part number will differ.