We have IBM ThinkCentre m52 8215-d6u PCs in 2 flavors of 1GB RAM and 4GB RAM. The 1GB RAM PCs read 0.98GB under 'my computer' > 'system properties'. The 4GB RAM PCs read 2.98GB, but it should read 3.98GB. The PCs are identical except for the extra memory. Why does not all of the RAM show on the 4GB PCs? How is this fixed?