Posted by: kurtsh | August 25, 2007

INFO: Why doesn’t my machine report a full 4GB of memory?

Have you ever installed a workstation with 4GB of memory and noticed that it only reports 3.0GB-3.5GB of memory available?

The reason for this is, assuming the chipset on the motherboard can actually address 4GB & many can not, that hardware has to have reserved memory address ranges to be accessed and these address ranges depend on the hardware memory requirements.  And since the 32-bit address space can only address 4GB, any hardware that needs to map address space to other uses takes away from the address space that’s usable by the system. 

For example, a monstrously powered video card may have 500MB of RAM that it needs to map.  This would result in a loss of 500MB from your addressable RAM, leaving a person with 3.5GB.  Other hardware in the system reserves that last .25 GB which would leave the system with 3.25GB of addressable RAM.

If you want to use the full amount of memory on a system, the solution is to use the 64-bit version of Vista.


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