Can you mix DDR2 and DDR3 on one motheboard?

Catishcat

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Apr 20, 2015
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My MoBo is P5KC, which is VERY old. I have 4gb of DDR2 RAM installed, and now I have a 2gb stick of DDR3 memory. P5KC supports both DDR2 and DDR3 (it has both slots, actually 4 double-channel DDR2 slots and 2 double channel DDR3 slots), but when I tried to install it, BIOS screen did not even show up. I removed this stick, and it worked perfectly well (I am writing this on that PC).

It's probably incompatibility issues between DDR3 and DDR2, because when I added additional DDR2 stick of 2gb, it booted up normally. Is this the problem, or I can do something about it?