Originally Posted by Torched-Geek
But what would the point of using the GDDR5 on the 256 bit bus? Just sounds like a ATI 4870 to me and they're already kicking around.
To get ahead of ATI in the terms of speed they would have to use GDDR5 on a 512 bit bus which would be extremely expensive.
They will be unable to maintain the 512bit mem bus from practical reasons @55nm.
To have 512 bit mem bus, well you need 512 pins on the chip only for memory access. These pins occupy some chip area. At 55nm the chip size will shrink to 60-70% of the 65nm size, where will they put the pins to access all the 512bit mem bus?
Unless they up the transistor count again (320sp?) to increase size, they will have to cut on those pins, and cutting memory to 384 or 256 bit is the most logical thing to do. Using DDR5 will compensate the memory bus bandwidth drop to keep an overall memory access bandwidth at the same, or even to up it at a higher level.
They've done it one time (G80 384 bit @80nm to G92 256bit @65nm), they can do it again.