cpu has fsb(front side bus) 用来talk with memory. dual channel现在amd何intel都有, 但amd不是真的support dual channel memory, dual channel only increase 3-5% performance for amd system. intel is fully support dual channel memory, it will increase 10-15% intel system performance. if ur motherboard suppport dual channel tech. 2*512 should faster then 1G. if motherboard does not support dual channel. 1 stick 1 G should faster than 2 sticks 1 G. for example, intel cpu now on is 800 fsb. so a dual channel memory best require ddr 400(ddr=double data rate). ddr 400 is the bus for memory, if u use 2 sticks (dual channel) it will be 800 total bus. it match the cpu fsb 800! that means how many data go to memory how many date go to cpu. normally pc3200 memory =ddr 400. 400 is bus , 3200 is speed of memory(hz). high hz is higher performance memory. if the same hz of memories, it will depend on latency of memory. lower latency memory is faster memory. for ddr , now on the best is 2-2-2-5. for ddr2 is 3-2-2-8. Memory 是很深奥的东西。 一般不用想太多!你就的price可以就行了!