Right now, ATI is using Samsung's 80nm 0.91ns K4U52324QE GDDR4 modules on its X1950 products. This is actually the slowest GDDR4 memory that Samsung sells, clocking in at a max of 1100MHz. Their 0.714ns RAM is capable of hitting 1400MHz which will be able to put future graphics cards beyond the 2.5GHz data rate and up near the 80GB/s range in memory bandwidth. Of course, the X1950 XTX memory bandwidth of 59.6GB/s is pretty impressive in itself.
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Anandtech