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9.4.6. 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 Fedora (2.6.27.19-170.2.35.fc10.i686)
root (hd0,1)
kernel /vmlinuz-2.6.27.19-170.2.35.fc10.i686 ro root=UUID=04a07c13-e6bf-6d5a-b207-002689545705 mem=1024M
initrd /initrd-2.6.27.19-170.2.35.fc10.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.
Itanium users must enter boot commands with elilo followed by the boot command.
Remember to replace xx with the amount of RAM in your system. Press Enter to boot.