ATI Radeon HD 4000 Series discussion

[trinibwoy]

No, diltech is correct, the data is mirrored on both memory banks, so while the cards do not render the same frame, when using sli you really only get the memory bandwidth and pool of one card

Gah! You guys are confusing the duplication of data on the framebuffer with memory bandwidth. They are two completely separate things!

I'm not sure how else to explain it but I'll try.

The duplication happens when the host CPU sends texture and other reference data to the GPU over the PCIe bus. This happens only when needed...if a texture is already in local memory on the GPU it's not resent. At this point both cards have the same data.

Bandwidth however is used to do the work to actually render the frame. Reading texture data into the chip, writing buffers back out to memory etc. This is not duplicate work as it's being done for two different frames. This is stuff a single GPU would have to do twice anyway so it's not wasted bandwidth.