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10.4.6. Is Your RAM Not Being Recognized?

Sometimes, the kernel does not recognize all of your memory (RAM). You can check this with the cat /proc/meminfo command.
Verify that the displayed quantity is the same as the known amount of RAM in your system. If they are not equal, add the following line to the /boot/grub/grub.conf: 
mem=xxM
Replace xx with the amount of RAM you have in megabytes.
In /boot/grub/grub.conf, the above example would look similar to the following: 
# NOTICE: You have a /boot partition. This means that 
#  all kernel paths are relative to /boot/ 
default=0 
timeout=30 
splashimage=(hd0,0)/grub/splash.xpm.gz 
 title Red Hat Enterprise Linux Client (2.6.32.130.el6.i686)
root (hd0,1)
kernel /vmlinuz-(2.6.32.130.el6.i686 ro root=UUID=04a07c13-e6bf-6d5a-b207-002689545705 mem=1024M
initrd /initrd-(2.6.32.130.el6.i686.img
Once you reboot, the changes made to grub.conf are reflected on your system.
Once you have loaded the GRUB boot screen, type e for edit. You are presented with a list of items in the configuration file for the boot label you have selected.
Choose the line that starts with kernel and type e to edit this boot entry.
At the end of the kernel line, add 
mem=xxM
where xx equals the amount of RAM in your system.
Press Enter to exit edit mode.
Once the boot loader screen has returned, type b to boot the system.
Remember to replace xx with the amount of RAM in your system. Press Enter to boot.