Dual channel RAM means that the motherboard uses two
memory controllers to tap into the entire bandwidth of two
sticks of RAM simultaneously. For example, your DDR266
RAM has a transfer rate of 2.1GB/sec (hence PC2100) but
your motherboard has dual channel memory controllers.
Your transfer rate is then 4.2GB/sec.
P4 RDRAM boards are dual channel. Dual channel DDR
on an nVidia chipset is the highest performance memory
system you can buy for the Athlon.
As to the actual RAM sticks, there is no difference. It is
just that you always need two to enable dual channel.
<i>It's always the one thing you never suspected.</i>