ATI Radeon HD 4000 Series discussion

[DilTech]

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.

This statement is correct regarding STORAGE.



This statement is incorrect regarding PROCESSING. A single card would have to do this job twice over two frames. Two cards do the same thing somewhat in parallel.



No it is not the same as a single 256-bit memory bus. It certainly isn't the same as a single 512-bit one either but it's definitely closer.

I quote you
but the gpu aren't doing the same job, because they are processing different frames
so they can use 90% of same assets, but doing different job at 100%

I'm going to break it down for both of you....

When using AFR, with 2x256bit each frame is limited to the 256bit bus of the gpu rendering it, just like a single 256bit bus. That's plain and simple. If a frame needs more bandwidth then the single 256bit bus offers, guess what happens? The gpu Chokes, on you guessed it, it's single 256bit bus. As such, even in AFR, 2x256bit is NOTHING like a 512bit bus.... With a 512bit bus, it has the full bandwidth available on every single frame.

See the difference? No matter how you break it down, or what claim you make, the fact is that 2x256bit just will not function like a single 512bit but rather closer to a single 256bit bus.