It was more important to get single sided with earlier AMD64 CPUs,
especially s939 and if you wanted to get 1T command rate. With more
recent
CPUs, AFAIK, the memory controller has been improved and according to
tables in the docs, it's more tolerant of multiple ranks at full speed.
It may still be a better strategy to start with single sided if the
intention is to increase mamory capacity later... and they you can find
them: here's a Crucial part
http://www.newegg.com/Product/Product.asp?Item=N82E16820146541 which is
said to be .8T (that is the clue for Crucial DIMMs with Micron parts) but
the pic shows the suffix as .M8FD which I believe is with Samsung parts -
funny thing is that the 2nd pic shows .16FG so who knows?? The .8Ts I got
from NewEgg a while back were indeed .8Ts and work flawlessly at
3-3-3-8(1T). The "scoop" on Web Forums is that the Samsung parts Crucial
is using are not as good as the Micron ones and may only run at 2T.<shrug>