Problems mixing memory modules

I have Asrock 4core1333-GLAN R2.0 motherboard and have been using 2X 1gb Corsair XMS2 5-5-5-12 800mhz DDR2 in dual channel mode.

I recently got hold of 2X 512mb Corsair XMS2 5-5-5-12 800mhz DDR2, and figured that i could use these on second memory channel and get 3gb of RAM which would be pretty optimal, since i run 32bit XP. I was a bit worried about mixing memory sizes and thought that i could lose dual channel mode.

Well, turns out i lose more than that. When all 4 modules are in, bios thinks that they´re all 512mb, giving me 2gb total and OS fails to boot. When i insert 2X 1gb + 1X 512mb one of the 1 gb sticks shows as a 512 mb and i get 2gb total again. Didn´t even bother trying to boot up OS. If i mix 1gb and 512mb modules in same memory channel, the computer won´t even POST.

Asrock manual says, that to use 4 modules, they all have to be identical but i didn´t believe them since mixing different memory sizes has worked before.

Is there something i could do in BIOS to get 3gb, or is this just unworkable situation?
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  1. Doesn't sound right unless that is a memory board specific issue. Also not familiar with 5-5-5-12 from corsair, they have 4-4-4-12, 5-5-5-15 and 5-5-5-18, I could be wrong, I have been before as it's marked on the calender.
  2. I solved the problem myself, here is the info if someone else runs into it.

    Asrock 4core1333-GLAN R2.0 supports 3 or 4 memory modules only if they are single sided. It only supports 2 double sided modules at any given time. Apparently my 1gb Corsairs are double sided and if i plug in additional modules while they´re installed, their capacity is halved. So, with any workable combination, i can´t exceed 2gb of ram. :(

    I guess that´s what i get for using budget motherboard... Still, i had never heard of this kind of limitation, but they actually tell it at Asrock web page. With very small font.

    Roonj: cpuz actually rates my memory 5-5-5-15 as you had said, but on the module is printed 5-5-5-12. Interesting...
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