Well, if your reply would be the rule for this Forum, 90% of topics would be useless (to you...)
More like 99.9% (to me personally).
However, I try to offer help when I can. Having a P45 system, I've been in this boat and have done the research.
Ask yourself the questions:
(1) Can you even find 4GB DDR2 sticks? (I couldn't, at the time)
(2) If I can find them, how much does 4 x 4GB DDR2 sticks going to set me back? (prices can vary greatly over time)
(3) Is the cost of 4 x 4GB DDR2 going to be more or less than DDR3 board + 4 x 4GB DDR3? (maybe have to factor in the time spent on replacing the board versus just adding RAM)
(4) What do I need 16GB of RAM in my P45 system for, other than bragging rights?
In the end, if all that comes out of it is a list of P45-compatible 4GB DDR2 RAM modules, that in itself will be worth the time to investigate, even if not to buy.
Good luck in your hunt.
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