Why does WinXP show half the installed memory?

By rschopp ·
I have a 10yr old PC (450mHz P3 - Win XP Home) which has given me great service. My problem is such: my AOpen AX6BC motherboard has 3 DIMM slots. In DIMM1 I have a 512MB module; in DIMM2 & 3 I have 128MB modules (768MB installed). The BIOS, POST screen & Everest (a system monitoring prog) show the installed memory in the range of 384 - 392MB. I ran memtest86+ and it also says 384MB of RAM - all the modules work in other machines. What's wrong?

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RAM Density

by TheChas In reply to Why does WinXP show half ...

The DIMMs you have installed in this system have too high a density for the BIOS and chip-set to address all of the RAM.

If you find DIMMs of each size with twice the number of memory ICs on them, the system should recognize the full installed RAM.

Keep in mind that you may also have a 256MB per slot limit on the amount of RAM that can be installed.

1 thing to try is just the 1- 512MB DIMM and then just the 2 128MB DIMMs. It is possible that you have a 256 MB per DIMM limit and the 512 DIMM is also too high a density. The motherboard may only see 128MB of the 512MB.

This happens because memory technology advances all the time. The memory design specification either allows for or is changed to allow new technology. Of course, that leaves us scratching our heads when we work on an older system with our stack of memory modules.


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If you look at the Users Manual or the M'Board Specs

by OH Smeg Moderator In reply to Why does WinXP show half ...

You'll see that it can not use more than 3 X 256 MEG RAM Modules allowing a Maximum Amount of installed RAM to 768 MEG.

You'll need Low Density SD RAM for this M'Board.



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