Hi all, I own an Oregon 550 (1 GB of internal memory) with a 4 GB Micro SD Card, Fat32.
In the internal memory, under /Garmin, I have:
gmap3d.img (from CN EU 2011.10)
gmapbmap.img (original map, non-routable)
gmapbmap.sum (?? don't know what it is)
gmaptz.img (from CN EU 2011.10)

While into the Micro SD, under /Garmin, I have:
CN EU_2011_10.img (full set, loaded with Mapsource 6.16.1 patched, unlocked with unlocker alternative New v.5.2)
G2-VEU012R.img found already unlocked
G2-VEU014R.img.xxx (found already unlocked - it seems that only one G2 can be seen at a time, so I have loaded both and add or remove the .xxx in one of them as required)
IT-TopoLand.img
TopoCH_2.img
The file names are exactly as listed, and it works perfectly. So I use these names to make sense to the content.
Cheers
Danilone