Dual Channel Memory

I Know if You have Say DDR3 and it is Single Channel Memory it works like this.

Every DIMM will be Accessed One after the other in order.

But if You have Dual Channel Memory Two DIMMs will be Accessed at the same Time then the next Two Dimms will be Accessed at the same Time.

Yes I Know the DIMMs are Installed in Pairs in Two Slots of the same Color.

But if the CPU can only take in 64 Bits at a Time why Access Two DIMMs at the same Time?