The Inquirer learned ATI's Radeon X1800 (R520) will have an internal 512 bit memory controller capable of using 512 bit memory. Samsung has this kind of memory available and an ATI prototype uses it running at 1600MHz.
Geforce 7800 GTX and all Nvidia 6800 generation cards are using 256 bit memory and 256 bit memory controller so this kind of comes as a surprise to us. ATI won't be able to take the full advantage of 512 bit memory and that the memory will operate as a 256 memory but will save some cost to ATI.The Radeon X1800XT will be clocked at 600MHz with 1400MHz memory so it possibly has lots of overclocking potential.
We don't know all the details but we believe that 512 bit memory controller can help you to use less chips on your board. I believe that you don’t have enough interconnections on the PCB to take the full advantage of 512 bit memory controller.