MSI 865PE Neo2-P Platinum Edition motherboard unable to detect 4GB Memory

I had been using the MSI 865PE Neo2-P Platinum Edition motherboard and it was working fine with 1GB memory. Today I have bought 4GB memory of Kingston. The maximum supported size of the motherboard was 4GB. But when I installed the ram on the mobo, the BIOS is not able to detect the whole memory. It is just showing 3GB as usable. i don’t know whether there is a latest BIOS to fix this issue and I never searched for it yet.

I don’t think so. Somewhere I have read that 32bit OS can address full 4GB memory but it completely depends upon the system and its chipset and also the processor you have installed on the socket. With Windows Vista SP1 Installed, you can see the full 4 GB ram but still lots are going to be miss. PAE basically allows the same but not sure about it all the time. The fact is Windows Vista 32-bit (including all editions) can handle up to 4 GB of RAM. But the actual address amount is less. But it is possible for you to force Windows vista to address and work with more than 4GB of memory but it needs Physical Address Extensions (PAEs). The alternative way is, you need to install x64 OS in any manner and you can go a little higher with your motherboard.

Also in some case, you can make use of the OEMs tweak to make the BIOS reserve less memory for platform use but it won’t be huge difference.

The memory remapping is only supported in 64-bit Windows. So you need to have 64-bit Windows installed in order to use all the 4GB of RAM. It is common that whenever you have 4GB of physical RAM installed, the system can only address a portion. It varies depending on the devices, chipset & BIOS. We called this behavior as a “memory mapped IO reservations". The Windows mask out residual physical addresses so that they cannot be used for working memory. The reservation goes for:

• BIOS – including ACPI and legacy video
• PCI bus and its bridges etc.
• PCI Express reserve at least 256MB and up to 768MB.

Intel chipset specs are good at default address reservation and in some cases it reserves nearly 1.5GB of memory but cannot be used by Windows in any manner.

Physical Address Extension (PAE) is important in this case because it has a capability to extend the physical address space to 36-bits but for that your hardware or chipset should have a support for this feature. The processor execution units will only see 32-bit addresses. The translation of 36bit addresses is handled by the MMU. The addresses will not get swapped over here, instead only the pages get translated. It is a feature of virtual memory in OS. If there is a PAE-able system in your case, it can handle up to 64 GB of memory. Do not enable the memory remapping feature in the BIOS because it will sometimes make the system ever worse. When it is enabled, even if you have 4GB installed, system will show only 2GB usable. OS has nothing do here.