http://www.beyond3d.com/forum/viewt...light=r9500+pro
Hi,
I’d just like to suggest a few things for you to test in relation to your recent 9500 PRO review.
I see that you have concluded that the 9500 PRO is a 4x2 based on the 3DMArk fillrate tests – IMO that conclusion is wrong. I’ll explain why…
First off, the architecture of Radeon 9500 PRO is an 8 pixel pipe card with a 128bit bus; now at 32bit 8 pixels all at once (and that’s not including other memory transactions such as Z checks etc) will require 256 bits of transfer, however with only a 128bit bus this is not sustainable and only the equivalent of 4 pixels per clock can be passed out. In multitexturing mode its not an issue as 8 pixels are produced in 8 cycles (not one per cycle, but 8 cycles pass then all 8 are ready to be passed to the framebuffer); in this instance only 4 pixels can exit in the clock they are ready, but the other four are stored in the fifo buffer, and because the pixel pipelines are still busy texturing the next set of pixels over several clocks, so the other four pixels are just passed out of the fifo on the next write cycle.
This is why the fillrate tests ‘appear’ to show 9500 PRO as a 4x2 card, but in fact all it is doing is balancing between the ‘loop-back’ texturing and how many 32 bit pixels can be written out per clock cycle. GeForce FX is also an 8x1 chip, but because it is also limited to a 128bit bus it will display very similar tendencies.
An easy way to test this is to run the 3DMark test in 16bit mode (16bit frame buffer and z buffer)….
Radeon 9500 PRO 32bit 3DMark Single Texture Fillrate: 937 MT/sec
Radeon 9500 PRO 16bit 3DMark Single Texture Fillrate: 1523.7 MT/sec
As you can see the fillrate in 16bit mode is greater than the theoretical maximum of a 4 pipe card running at 275MHz. If you also test a 9700 (non-pro) you’ll see that this fillrate is very similar to its 32bit fillrate.
This also throws into question your conclusion that it is a 256-bit board. However, IMO this was on fairly shaky ground in the first place. Concluding that it is 256bit based on AA performance may not actually be possible with chips such as R300 – R300, like GeForce FX, features AA colour compression so it will be very difficult to assess exactly how much bandwidth is being used. Its also clear from the board layout that the power regulation circuitry that there is no memory traces going to the right hand portion of the chip, which is where two of the four 64bit memory controllers of R300 are located – all the memory traces of the 9500 PRO go to the top portion of the chip, meaning it only goes to two memory banks.
Cheers,
Dave Baumann
Editor-In-Chief
http://www.beyond3d.com