I am using a Dell Vostro 1700 laptop which currently has 2GB of RAM. I was considering buying some more memory to upgrade it to 4GB. I am running 32 bit Windows Vista and I know that there can be issues that prevent it from making use of a full 4GB which I believe relate to the fact that memory mapped devices, e.g. graphics card, also need to be allocated addresses in the 4GB range addressable with 32 bits.

Consequently I was looking at device manager -> resources by connection -> memory to see what devices where allocated what memory addresses. I was surprised to see that there was an entry for [80000000 - F3FFFFFF] PCI bus. That is a 1.8GB range of addresses. When I expanded it the only thing in it was [E0000000 - EFFFFFFF] NVIDIA GeForce 8600M GT which is only 256MB.

So my question is does the PCI bus really occupy 1.8GB of address space and will it prevent my computer from making use of any more memory than it already has.