Out of 4096 mb physical memory, only 3840 are available, where did 256 go?

Question

linux

Hello, I have one ancient computer, but for some reason only 3840 of 4096 memory are available on it . CPU

: Intel quad q8300.
Motherboard: p43 neo.
GPU: amd radeon 7770 hd.

I tried to dig into the bios but didn't find anything, does anyone have any idea how to use all the memory? Operating system x64.
Previously, there was another motherboard, 4 gigs were available on it. Probably something needs to be changed in the BIOS, but I'm not sure.

Answer 1

https://answers.microsoft.com/en-us/windows/forum/...