Troubleshooting memory not seen by the operating system issues - Servers and IntelliStation

Resolving The Problem

Symptom

The correct amount of physical RAM memory installed in the system is displayed correctly during the POST/startup memory count, but is not all seen or displayed correctly within the operating system, once it has loaded.

Solution

Please check the operating system limitations on addressable memory amounts. Some operating systems cannot address memory amounts over a certain amount or may require an update or software change to use large amounts of RAM memory. Be aware of the differences between "physical" installed memory and "available" memory, as "available" memory may differ from machine to machine even though they both may have equal amounts of "physical" memory installed.
 
For example: A system running Microsoft Windows 2000 with 4GB of physical memory installed will show approximately 3.5 to 3.7GB of RAM available. This is because the operating system is not counting memory reserved for PCI resources as user available memory. PCI resources include: onboard ethernet devices, onboard audio devices, PCI/AGP video adapters, etc. Typically machines with more devices installed will have more memory reserved to operate these devices.

When adding additional RAM memory (Dual Inline Memory Module or DIMM) to an IBM system, it is essential that the memory be tested and certified as being supported for that specific IBM machine type-model. Most 3rd party memory does not meet the stringent performance and quality guidelines required by IBM, and thus is not supported in any IBM systems. Please check the IBM ServerProven compatibility Web site for the correct part numbers for each system's memory.

Note: Large memory support is available in Microsoft Windows Server 2003 and in Microsoft Windows 2000. See article from Microsoft.

If memory is reported correctly during the POST memory count, but some of it is not seen in by the operating system:

1. Check the operating system's limitations on addressable memory amounts. Some Operating Systems cannot address memory over a certain amount or may require an update or software change to use large amounts of RAM memory. Please go to the software vendor's Web site for this information.
   
   
2. If running Novell NetWare 3.x or 4.x, you have to manually register memory over 16MB (3.x) and 64MB (4.x with no Support Packs) to have it seen and used by the Operating System.
   
   
3. Microsoft Windows 2000 Advanced Server and Datacenter Server will not recognize memory above 4GB without the /PAE switch appended to the BOOT.INI file. Here is the procedure for this:
   
   
   1. Click Start, and then click Run.
   2. Type C:\boot.ini, where C is the drive letter of the location of the boot files: Ntldr, Boot.ini, etc).
   3. Modify the line that corresponds to the specific operating system by appending the switch /PAE.
   4. Save the file, and then restart the system.
      
      
4. Microsoft Windows NT 4.0 Server is limited to 4GB of total addressable memory. For support of more than 4GB of memory, NT 4.0 must be upgraded to Windows 2000 Server, Advanced Server, or Datacenter. These versions range in memory support from 4GB to 64GB.
   
   See: Windows NT 4.0 will not install with more than 2GB of memory
   
   
5. Linux distributions running the 2.2.x kernel may not be able to address memory amounts above 1GB. Updating to the 2.4.x kernel raises the limitation to 64GB. Please see your Linux vendors support site for instructions on updating the kernel.
   
   
6. If, after trying the tips above, an operating system is still unable to recognize or use the total physical memory that is installed and seen during the POST memory count, please contact the operating system vendor for more support.