Quote Originally Posted by GPSFranz View Post
3. Why do some IMG files contain unlock codes (i.e., why are the unlock codes in the IMG file, not just in a separate .unl file)?

4. Is a separate .unl file required, even if an IMG file contains an unlock code?

5. If a separate .unl file is still required, do the unlock codes in the IMG file and in the separate .unl file have to be identical (or can they be different, yet both valid unlock codes for a given GPS unit or SD card)?

6. What software product puts the unlock codes in the IMG files, and when (or under what conditions) does it do so?

7. Why and when (or under what conditions) does an IMG file contain more than one unlock code?
These questions and answers are off-topic, but here we go anyway.

Historically, a Garmin MapSource product was shipped in CDs/DVD along with an unlock code on a yellow sheet or sticker. To use the map, you must install it on PC and enter the unlock code to unlock it so MapSource.exe can read and display it. To install the map into your GPS device, you select the map tiles you want and MapSource.exe will generate the file gmapsupp.img with the unlock code embedded then writes to your device.

If you select map tiles from more than one MapSource products then the resulting img file will have more than one unlock codes embedded, one for each product. You can display, add or delete embedded unlock codes in an img file by GMapTool. This kind of unlock code is tied to the unit ID of your device such that the map cannot be used on other devices.

Then, Garmin sells pre-generated maps in SD cards. Each card has one map file and one .unl file. The latter contains an unlock code tied to the ID of the SD card. This allows the map to be used when the original SD card is inseted on other devices. However, the map and unlock code will not work if copied to a different SD card due to different SD card ID.

A .unl file can have multiple unlock codes. Just join them together without space and end-of-line in between. Each unlock code can be tied to the unit ID or SD card ID. Most SD card savvy firmware will read in all unlock codes, regardless of location (embedded or .unl files) and ID type (unit ID or SD card ID). A map will be unlocked if at least one of them is valid and matches the map product.

Later, Maps pre-installed in a new GPS device or sold/upgraded by downloading also take the .unl approach.

Lastly, new maps sold and downloaded are protected by the GMA scheme. On devices with old firmware, it is still possible to unlock them by either method above. On new devices with GMA savvy firmware, they can only be unlocked by a valid .gma file or an unlocker tool. Also, for completeness, the MMR subfile for cityXplorer cannot be unlocked by an unlocker tool. Change of MapID and .unl are required.