Hi Merry Map makers

Can anyone tell me the file structure type of this handheld gps uses, is it Garmin or .System ??

As I want to build a SD card for extra maps ready for the arrival of the eTrex Legend® HCx.

My understanding is Max of 2 maps for Garmin as Garmin / gmapsupp.img and gmapsup1.img and many maps for .System as Map / xxx.img

I know I am just a big kid who can't wait to plug it in and play!

Kind regards and Thanks