Probably smokefree was talking about service mode firmware as .rgn format to flash in case of corrupted firmware recovery (System software missing or hard bricked device)
In these cases pc doesn't see the gps, so flashing in preboot with Updater.exe is the only chance to revive it.
More here:
[Only registered and activated users can see links. ]
Updater.exe is an old soft, it was the standard flash utility for old Garmin devices.