Member Avatar for mgrunge1967

I have individually checked each RAM chip I have and each slot on my mobo. I have 4 1GB Ram chips that work together in all combinations up to 3GB but when I use all4 it is only giving me 3.25GB. My mobo is capable of 8GB whit 4 slots ( 2GB per slot ). On boot it shows the full 4GB of RAM but in Windows XP professional OS, the system only shows the 3.25GB. If anyone can explain to me why this is and what I can do to get my full 4GB I would greatly appriciate it.

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Short answer: nothing is wrong with the RAM sticks — this is how 32‑bit Windows and PC hardware address space work together. already verified the modules and slots; the reason Windows XP shows ~3.25GB while the BIOS reports 4GB is that some of the top of the 4GB physical address space is taken by memory‑mapped I/O for PCI/PCIe devices (graphics cards, chipsets, etc.). That reserved region simply overlaps physical RAM addresses, so the OS cannot use those bytes.

How to verify what is being reserved: run msinfo32 (System Information) and open Hardware Resources → Memory. The list shows address ranges and which device owns each block. Large contiguous reservations near the top of the 4GB range point to BARs/MMIO. Try removing or reseating add‑in cards to see changes. Check the motherboard BIOS for a “Memory Remap” or “Remap Memory Hole” option and update the BIOS if the option is missing — enabling remap moves the unusable area above 4GB so a 64‑bit OS can use it.

Practical fixes: (1) Install a 64‑bit OS (Windows x64 or a modern 64‑bit Windows) to access the full 4GB — XP x64 exists but driver support is limited; modern x64 Windows versions are preferable. (2) If you must stay on 32‑bit XP, the only realistic choices are to reduce the space hardware needs (change video card or disable unused controllers) or accept the ~3.25GB usable result. PAE is not a practical client‑XP solution — server SKUs or special builds handle >4GB, but client XP is effectively capped.

As said, the ~3.25GB result is common. Given your DIY GigE board and discrete PCIe devices, this behavior is expected and not a bad DIMM or motherboard failure.

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Member Avatar for Xpenetrator

Yes. Read here: or google "memory limit XP". I felt surprised, too. :)

Member Avatar for mgrunge1967

Yes. Read here: or google "memory limit XP". I felt surprised, too. :)

Wow, i guess I will load my x64 version. But what I still don't understand is that I only get 3.25GB and not the 4GB it still seems it should be capable of. Even with all that I shouldn't have an issue with the restriction of my memory. Thanks a lot for the article and the quick response.

Member Avatar for Xpenetrator

You're welcome :)
You might find this whole thread interesting:

And according to the Google hits, 3,25GB is a very common amount in this concern. Maybe you have onboard graphics?

Member Avatar for mgrunge1967

definitly no onboard graphics, I built the systam myself on a gigabit mobo with the duel express 16x slots. but I do see what you mean with the google hits, you have been a great help to me, thank you.

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