[CentOS] Memory recognition in 6.2

Hi All:

I have an HP DL380G5 server which I am loading CentOS 6.2 on and it does
not appear to recognize all of the RAM installed on the server. The BIOS
is reporting 26GB however top is reporting:

  Mem:  15720140k total, 418988k used, 15301152k free,  30256k buffers
  Swap: 17956856k total,      0k used, 17956856k free, 135536k cached 

and free is reporting:

               total   used     free shared buffers cached
  Mem:      15720140 418848 15301292      0   30256 135536
  -/+ buffers/cache: 253056 15467084
  Swap:     17956856      0 17956856

I have tried adding the mem= parameter to the /boot/grub/grub.conf file
as in:

  title CentOS (2.6.32-220.17.1.el6.i686)
          root (hd0,0)
          kernel /vmlinuz-2.6.32-220.17.1.el6.i686 ro [SNIP]
          initrd /initramfs-2.6.32-220.17.1.el6.i686.img
          mem=26624M

but this has not appeared to work.

Any suggestions would be gratefully appreciated.

TIA

Regards, Hugh

-- 
Hugh E Cruickshank, Forward Software, www.forward-software.com