Red Hat Knowledgebase

Release Found: Red Hat Enterprise Linux

Symptom: The computer correctly sees all the physical memory during POST, but the operating system does not recognize all the installed memory. The memory has been verified as good. Passing value of the physical RAM to the operating system during bootup (either via GRUB or LILO) does not seem to change anything.

Solution: This is most likely due to the operating system not counting memory reserved for PCI resources as user available memory. This is not a defect on the part of the operating system.

PCI resources may include but are not limited to onboard Ethernet devices, onboard audio devices, PCI/AGP video adapters, and other PCI devices installed in the system. Typically machines with more devices installed will have more memory reserved to operate these devices. Be aware of the differences between "physical" installed memory and "available" memory as "available" memory may differ from machine to machine even though both of them may have equal amounts of "physical" memory installed.