in new garmin unit like nuvi 3790, we need to create a folder and name it as "Map" and put all the map inside it. no need to put name as gmapsupp.img just rename it as u like xxxx.img. this method can be use either u use memory card just create the folder name it as "Map".
where to put the mp3 file need to create a folder or not.
if we have the jcv file like the old garmin cn 2010.20 where to put in the memory card or just put it in garmin\.system\jcv