Dimension 8400 Windows 7 64 bit sees 4gb but uses 3 GBof DRAM

derekjeter

Version A06 has 'Improve support for 64-bit operating systems' and the latest BIOS update for the 8400 is A09, released 8/14/2006.

See HERE

Bev.

I installed A09, there was no change.  Any other suggestions.

Thanks

derekjeter

Sorry, no more suggestions, maybe another member has some and can step in.

Bev.

Unfortunately, it requires hardware support as well as software/firmware support to make use of 4 GB of installed DRAM.  Please see this:  System Unable to Address All of 4 GB Installed RAM.

The short version is that the chipset must be capable of supporting 8 GB of RAM, the processor must be 64 bit capable, the OS must be a 64 bit version, and the BIOS must support memory remapping.  The show stopper for the Dimension 8400 is the chipset; the 925x/925xe can support a maximum of 4 GB of address space.  I'm sure that the BIOS doesn't support remapping also since it would not make sense to have the remapping capability for a chipset that will not support it.

Edit:  While the knowledge base article specifies Windows Vista, the problem is the same for Windows 7 since the process for making all 4 GB of RAM usable is the same in both Vista and Win 7.  The computer can't move the hardware addresses out of the way of the memory located in the top 1 GB of address space, so it is necessary to remap the memory to the area above the 4th GB of address space.  If the chipset can't count that far, the OS can't perform the necessary remapping.

You can upgrade to 3 GB's of ram, but the pairs of chips should match for best speed--matching 1 gb in slots 1 & 2 and 512mb in slots 3 & 4.