Beyond3D has posted a review on the GeForce FX 5900 Ultra Reference

One of the most obvious differences between NV30 and NV35 is that the memory bus interface has been increased from 128-bit to 256-bits in width. NV30's bus was similar to GeForce 4 Ti's, with four 32-bit "crossbar" busses, but utilising DDR-II memory as opposed to DDR. NV35's bus utilises four 64-bit busses and is said to operate with both DDR and DDR-II memory types, but the first board implementations will utilise DDR memory.

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