ATI Radeon HD 4000 Series discussion

[darkskypoet]

8 gb in either direction.. equals 16gb/s total. Yes. each GPU has 16 lanes to bridge chip, so 16GB/s total bandwidth between each gpu and bridge. Yes. and 16GB/s total bandwidth between bridge and system PCIE Switch. Yes.

No, there is no half of it is shared with CPU... Whatever is required to be passed through to / from cpu, memory, etc goes through bridge to one or both GPUs. It's not hard set.. Period. Add to that the bandwidth available over CF side port. So You're right cpu uses some bandwidth, gpus use some bandwidth, but this half stuff isn't true. As well, the GPUs can use their full 16 lanes to talk to each other as needed, and only need to cede lanes to incoming / outgoing data as necessary. One of the advantages of having a fully programmable 48 lane PCIE 2.0 switch on the card, is that you get the flexibility of adapting to data as it flows, no having to hard set anything like this. As well, the switch features some built in QoS features which would assist in the shaping of traffic between gpus, and between system and gpus.

So what were you trying to say Shintai?

In fact... might as well check this out... Here is a white paper on a chip like this in a graphics setup... Kind of neat if you care to read it: http://www.plxtech.com/pdf/apps/ExpA...cs_07Mar07.pdf I think it's actuall the one used on the 3870 x2. If I have my model numbers right, but it also supported dual cast, and low latency ops among other things.