Quote Originally Posted by syzygy View Post
From what I can see, the main reason is indeed to save space, a 25% saving. By design, Garmin reserved some areas in their img header for future use and expansion. As time goes, these reserved areas gradually become defined and used. The 9-byte part number at offset 48 is just one example. It is obvious that you want to minimize the use of reserved areas as much as possible so there are more rooms left for the future.
I totally agree with this analyse: Garmin wants to save space, not in the whole img but in the header.