At DDR400, that's 1 DIMM per channel, so maximum 2 DIMMs.
At DDR333, that's 2 DIMMs per channel, so maximum 4 DIMMs.
Expect any unstable system if you do otherwise.
I believe this ignores another relevant factor: how many chip-selects
the dimm uses. my understanding is that if a dimm is "double-sided",
it means that it uses 2 CS's. table 46 on p 182 of AMD's bios guide
(doc 26094) appears to allow up to 6 ranks for ddr400/2T operation.
afaikt, a double-rank dimm is AKA double-sided. unfortunatley AMD also
adds some weaselish text about how MB vendors should validate, etc...
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