Why do iOS devices have both UDID and Serial Number?

Question

Why do iOS devices have both the UDID and serial number?

Are they not the same; a number that uniquely identifies a device?

Answer 1

No They are not same.

Serial number is Just a hardware device number that use for warranty claim of device. Its just like IEMI number of device

And UDID is hidden number to use for device testing its a unique key that is stored in apple database.