With the new NForce, Granite Bay and SiS655 chipsets now available we now have this thing called Dual Channel DDR. Here is a 'general idea' behind Dual Channel DDR as it relates to the P4. (works fairly well for AMD as well...just adjust the CPU FSB value) The difference in single channel operation and dual channel operation is in the way the motherboard uses the memory...nothing to do with the memory modules itself. For DCDDR to work you need to have two modules of memory, ideally the same size and specifications for optimum compatability. Dual channelling has been done for some time already...it's the way almost every 16bit RDRAM P4 setup runs...Dual Channel... you need to have your memory run in pairs. Interestingly enough RDRAM now has a 32bit Single Channel version available (though not widely adopted). Imagine your mobo is like a factory. There is the CPU on one side and the Memory on the other side. Both areas work at certain speeds. Both areas have data for the other to work on. Each area has a door that is a certain width to allow data to come and go and a rate at which the work can enter/leave. The CPU operates at 533mhz (fsb) and has an access door that is 8bytes (64bits...there are 8bits in one byte) wide. 533mhz x8 bytes = 4264mb/s. This is the theoretical amound of data that can pass through to the CPU per second. In Single Channel DDR operation all the memory is in one room and there is only one access door or one channel that is 8bytes (64bits) wide. Let's say the memory is set at 333mhz. 333mhz x 8 bytes = 2664mb/s. This is the theoretical amount of data that can pass through the memory per second. This rate is lower than what the CPU can potentially put out, therefore the CPU waits for the memory. In Dual Channel DDR operation it's like the memory is in two separate rooms with two access doors or 2 channels, each 8bytes wide (16bytes or 128bits total). The memory is at 333mhz. 333mhz x 8bytes x 2= 5328mb/s. This is the theoretical amount of data that can pass through the memory per second. Double that of what was available in single channel operation. The CPU isn't waiting any more. Granite Bay uses a default DDR266 in dual channel. 266x8x2= 4256mb/s ...almost matching the 533fsb CPU's bandwidth perfectly. As the P4 moves up to an 800mhz FSB, DDR400 will become the matching memory for this CPU. Don't expect miracles with all of this increased memory bandwidth though...it does improve overall performance as there aren't parts waiting around for each other, but that increase in performance doesn't fully reflect the 'doubling' of available bandwidth. There are other forces at work too...latencies, timings, inefficiencies etc. Consider that current single Channel DDR333 and 400 setups can run within 5-10% of RDRAM and DCDDR setups despite their memory bandwidth disadvantage. Various applications will benefit more/less than others for each setup. I see the main advantage of Dual Channel operation is that it relaxes the need for running DDR at very high speeds.