Fast memorychips vs 512bit bus

[Dutch Guy]

Much of the price of a new videocard is because superfast expensive memorychips are used, but why don't they use a 512bit memorybus instead as that would instantly double the memory bandwith?

Or am I missing the obvious?

 

[Dutch Guy]

...and it requires a hell of a lot of extra transistors.

Good point, I knew I was missing something obvious, that combined with the investment.

But what I did notice is that a lot of videocard are bandwith limited in situations, this for instance:http://www.beyond3d.com/reviews/bfg/7800gtoc/index.php?p=13

The maximum performance increases we see here are around 9%, which mirrors the bandwidth improvement from the memory overclock.

Indicating that a 7800GT is bandwith limited so a doubling of memory bandwith would possibly mean a lot better performance

 

[Dutch Guy]

Isn't the memory controller on the X1900's 512bit but only connected externally at 256bits for the memory chips.

Yes, after I saw yout rpost I went back to a X1800 review explaining that here: http://www.anandtech.com/video/showdoc.aspx?i=2552&p=4

But I will look at it again a bit later as it is way too difficult early in the morning

For quite some time, the high end in graphics memory architecture has been a straight forward 256-bit bus divided into four 64-bit channels on the GPU. The biggest issues with scaling up this type of architecture are routing, packaging and clock speed. Routing 256 wires from the GPU to RAM is quite complex. Cards with large buses require printed circuit boards (PCBs) with more layers than a board with a smaller bus in order to compensate for the complexity.