Problem with RAM on Lime2

[PikOpaT]

Hi,

I recently discover that only half of the DDR3 is used by my Debian on a Lime2. When I run the free command, I have this

Code Select Expand

total       used       free     shared    buffers     cached
Mem:        509704     411096      98608      14328      52408     222204
-/+ buffers/cache:     136484     373220
Swap:            0          0          0


I use a Debian GNU/Linux 8.9 (jessie). I set the Lime2 to work as a "Internet Cube". It uses YunoHost.

Do someone know why my system only use half the memory and how I can fix that ?

Thanks in advance, many thanks !