On a CentOS 6.7 machine, after adding 2 additional 1 GB RAM modules, the total RAM detected was:
3044204k (as returned by command 'top').
There were in fact 4 identical modules of 1 GB installed, and also showing up in the BIOS.
The reason was another setting inside BIOS: for some reason : ADVANCED --> CHIPSET CONFIGURATION --> Memory configuration
was set to "Manual - User defined", instead of "Automatic",
and the RAM speed was set to the same value 800 MHz as the system speed.
After setting to "Automatic", the value was reading as 667 MHz (which was corresponding to the value on the RAM modules).
Hope this info is helpful some day for someone running into the same problem
Total RAM is less than total RAM installed
Re: Total RAM is less than total RAM installed
If you have centos 32 bit, just use PAE kernel.