ATI Radeon HD 4000 Series discussion

[darkskypoet]

I was hoping for something along the lines of how quad core CPUs do inter-core communication. Although in that case all the cores are on the same die. But I was still hoping for something along those lines. I don't know much about CPU/GPU architecture so it is difficult for me to speculate realistically. Is it really theoretically impossible to have seamless multi-GPU communication? Also why would the GPUs on the 4870x2 need to use the motherboard-based PCIe bus? The two chips are right next to each other on the same PCB.

Mainly because they get every single last bit of information they will ever process in through the PCI Express bus. Inter die communication aside, they need a way to efficiently talk to the rest of the system. that's why a bridge chip is necessary. Only other option is to daisy chain the chips so that one acts as arbiter on the PCIe bus, then forwards info.. but that would be a bottle neck, and would waste precious inter die B/W when there is already transistors on the die to handle incoming and outgoing non local (to the card) xfer of info.. PCI express.

Thus... regardless of inter die comms... two chips, equals bridge chip for system requests from / to cpu, and system memory, and stuff