Help! Power Mac G4 MDD won't recognize 512 ram

[DinoAdventure]

I bought a 1.25 GHz Dual Powermac G4 MDD from my work, and I'm trying to add ram to it. It came with one 256 stick which it recognizes no problem, and I added another 256 stick that it also recognizes. Problem is, whenever I try to add a 512 stick it won't recognize it. I have tried 3 different 512 DDR sticks of various brands in every slot and it just won't pick them up in the system profiler. I tried resetting the PRAM twice (command option P R on startup) and no dice. What gives? I've done a lot of searching and I see no reason why I shouldn't be able to use 512 sticks.

Thanks for the help.

edit: forgot to mention that it's running 10.4.8

 

[AlexMaximus]

Size matters...

Hi Dino,

since the G4 MDD is really a server type of computer (Xserve technology) the G4 dosn't like any mix of ram. Did you try to use the 512 ram modules only?
Do not mix 256MB and 512MB and on top of that use the original Apple recomended model. Otherwise you may run into moduls with the incorect speeds/cycle times (333, 322, 222) you know these tact cycles. Hopfully it works. Good luck