They are lots of reasons why.
The major one will be the ram. If it is double sided ram, then the maximum the board will take is 2 X 1Gb modules.
If the ram is single sided then the motherboard can take 4 X 1Gb modules but you have to alter the memory timing in the bios. It has to be changed from 1T ( command per clock) to 2T. Also the memory voltage has to be altered to 2.8v.
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