NVIDIA 'Fermi' GPU Architecture Revealed @ Tech Report

"Six of the darker blue blocks on the sides of the diagram are memory interfaces, per their labels. Those are 64-bit interfaces, which means Fermi has a total path to memory that is 384 bits wide. That's down from 512 bits on the GT200, but Fermi more than makes up for it by delivering nearly twice the bandwidth per pin via support for GDDR5 memory."