I've installed 2x 1 GB and 4x 512 MB memory into my GA-8KNXP system which would sum up to 4 GB. The specification from the manual says:

Maximum memory support: 4 GB. If all six slots are utilized, slot 5+6 may only equipped with single-sided RAM modules.

And so I did.

Anyway: The BIOS counts up to 3.5 GB and finishes there. Also my Linux system reports only 3.5 GB of memory although 4 GB memory support is activated in the kernel.

So I suppose this is a memory mapping issue or a hardware issue. I've tried removing only on of the 512 MB memory modules leaving 5 modules in place. But that just stopped the system from powering on correctly (screen stays black although fans and leds come to live). Dual Channel was detected and enabled so the system technically found all 6 modules.

"dmidecode" in Linux reports only memory in slots 1 to 4 and ignores slots 5+6, so it only detects 3 GB of memory. It also says the system would support up to 16 GB of memory with 4 GB modules per slot. I think technically the chipset should be able to offer and utilize the complete 4 GB memory range.

Any clues what else I could check? Or do I have just to live with 0.5 GB wasted memory?