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WTF is this s**t?!

AMD Tech Support said:
Dear Customer,

Your service request : SR #{ticketno:[8200300964]} has been reviewed and updated.

Response and Service Request History:

We understand you have a question about running 2 different specifications video cards in crossfire. The result is the faster card will downclock to the slower card. It is recommended to get identical cards from the same manufacturer for performance.

For example, HD5770 700mhz gpu clock 800mhz memory GDDR5 and HD5770 650mhz gpu clock 700mhz memory GDDR5. The slower will not be able to run at the speeds of the faster card because it will be running beyond it's design specification and there the faster card will need to downlock to 650mhz gpu and 700mhz memory speeds.

In order to update this service request, please respond, leaving the service request reference intact.

Best regards,

AMD Global Customer Care

I think I know where this whole 'downclocking' rumour started.

Anyway, I'm gona run my own benches and prove them wrong. :)
 
lol sounds right to me, i would of thought anyway that the other couldnt cope with other higher gpu speeds
 
lol sounds right to me, i would of thought anyway that the other couldnt cope with other higher gpu speeds

Here comes my extended explanation... prepare yourself...

Actually, this is not the case. You need to think of the way CrossfireX works. It works with Alternate frame renderings, synchronized via the card's Crossfire plug or through the motherboard on some cards. Every tame a frame is rendered, it has to be synchronized to the main card's framebuffer in order to be displayed. The way the crossfire system is designed, it must pass through every card in order to do this (AMD decided this was the simplest route) and thus is synchronized to every framebuffer along the way. This will cause the card with the slowest memory to become the bottleneck, because things have to be synchronized to it before they can be displayed. There will not be memory downclocking, just bottlenecking. As far as core clocks, The frame renderings alternate. One GPU could take 5 times as long as the other, it does not matter, but as soon as it pumps that frame out, the next card is rendering the next frame in the sequence, and it begins the frame after. Basically, there is no need for any form of downclocking in the current AFR crossfireX model, though this does not prove that AMD did not do it anyway.

This on the other hand, does prove it.

codmw2.png

If the faster GPU is running at the clock speeds of the slower GPU, then most of these benchmarking results are not possible.
 
The thing about the message from AMD is that they thought you were talking about the same cards with different speed (an regular card with an OC'ed card), or so it seems.
 
The thing about the message from AMD is that they thought you were talking about the same cards with different speed (an regular card with an OC'ed card), or so it seems.

Yeah I know, which is not even the question I asked, but the same explanation applies in that case too.
 
Then the stream processors is what's making the difference?

I ripped a CD in 2 different formats, one in FLAC, and the other in MP3 128Kbps. I can't seem to hear a difference. I'm assuming it's more of my hardware than the formats. That, or that my ear can't hear a difference.
 
Then the stream processors is what's making the difference?

I ripped a CD in 2 different formats, one in FLAC, and the other in MP3 128Kbps. I can't seem to hear a difference. I'm assuming it's more of my hardware than the formats. That, or that my ear can't hear a difference.

No, the SPs would not account for such a large difference.

You're using a CD as a source. There's your problem.
 
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