Why does Linux Ubuntu not see 4GB of RAM?

Question

linux

Installed OS Linux Ubuntu 14.10 LTE x64. At first it showed 2.4 GB of RAM, now 1.9 GB. The computer has 2 samsung modules of 2GB each. How to fix?

Answer 1

command output here
and
sudo dmidecode --type 17

Answer 2

Maybe /tmp is mounted in RAM.

Answer 3

The question is very informative))) 1 we don’t know what kind of video you have, does it eat RAM or does it have its own 2 is all memory visible in the BIOS 3 did you check it with memtest