dual channel RAM uses 2 DDR RAM disks, and tries to transfer data to and from them both at the same time to theoretically give double the performance.
dual CPU's and dual grapics cards: basically, 2 pieces of hardware that work together on one thing, or independantly on their own tasks. this would theoretically give double the performance
but notice the word theoretically I used. usually it does not give double the performance
conditions are usually not perfect, and that means it cannot run to its full potential
while theoretically dual hardware would give 2 times the performance, that is only at its best (which is practically never). most of the time it gives about 150% of the performance of single hardrare, and sometimes not even that
ther are many reasons why this is so:
* sometimes they have to communicate with each other, which makes it slower
* sometimes the programs you use are not optimised for dual hardware
* sometimes (in the case of RAM) more data is needed from one RAM disk than from the other, so the other RAM disk doesn't transfer as much, therefore less is transferred in a certain time
* a lot of the time dual hardware creates higher latencies
* sometimes the other hardware bottlenecks the dual hardware
and there are probabbly more I haven't thought of