SG105rev1 flashed to XG105 memory limit

Hello,

I've a SG105 rev 1 which has been flashed to XG a several years ago.

I've replaced the internal 2GB memory by a 4GB PC3-12800 memory to increase total memory and pray to be able to upgrade from firmware SFOS 17.5.14 MR-14-1 to v18.

But after memory upgrade, the XG see only around 3 GB of RAM. Why ? it's not an 32 bits unsigned integer limit (4GB) not a signed integer limit (2GB).

Is this a volontary limitation to force to buy a new device ? #NotEcological. I'm alone in the desk, no need to replace my router.

Thanks,

Vincent