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Old August 17, 2008, 09:14 PM
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Default 4870X2 Crossfire " SIDEPORT" xsp

interesting stuff yet unused features,didn't see this else where in the forms
source techPowerUp :: Sapphire HD 4870 X2 2048 MB Review :: Page 1 / 28

wonder what performance gains will be realized when that's turned on

"One novel feature of the HD 4870 X2 is that it has an additional direct-GPU-to-GPU interconnect called CrossFire Sideport (XSP). The XSP offers an additional 5 GB/s interlink bandwidth between the GPUs but is not enabled at this time. Yes, you read correctly. The official reason why the XSP is disabled at this time is because that much bandwidth is not required with current applications and it will be enabled at some point in the future via driver update.
One major advantage of the XSP that I see is that transfers between the GPUs would have a lower latency. The Gen2 PCI-E bridge will certainly be fast, but it will take a short time to process the incoming data and send it out to the other GPU (<140 ns). With the XSP's point-to-point interlink this delay is eliminated. So my speculation is that AMD is working on using the XSP feature but the driver support simply doesn't work as intended at this time."
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Old August 18, 2008, 01:20 PM
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Here's the same link I posted in the HardOCP thread, 4870x2 XSP Sideport feature poised to counter rumored 280gx2 - [H]ard|Forum which I assume you saw already, if not what a strange coincidence, very strange...

AnandTech: AMD's Radeon HD 4870 X2 - Testing the Multi-GPU Waters

So what's the deal hear exactly, is it ever going to work? Feature that wasn't able to be implemented upon release or had diminishing returns that didn't outweigh power consumption requirements? Some info from ATI would be nice.

From what anand says I get the feeling that it will never be implemented regardless if it can be turned on apparently at will. Perhaps a future revision will make use of it.
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Old August 18, 2008, 01:32 PM
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It is a weird thing indeed. I'm thinking that since right now they can't share the data between them, they process it by half the amount. Perhaps if they do enable, it will allow communication between the two GPUs and memory to allow faster processing. I don't understand why they wouldn't put in the PLX 2.0 chip if they're not going to use it...they could've saves a lot of money if they kept the same PLX chip in from the 3870X2. We'll see though because there's no word of a GX2 from Nvidia yet.
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Old August 18, 2008, 08:56 PM
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Quote:
Originally Posted by Windego View Post
Here's the same link I posted in the HardOCP thread, 4870x2 XSP Sideport feature poised to counter rumored 280gx2 - [H]ard|Forum which I assume you saw already, if not what a strange coincidence, very strange...
nope never saw the hardocp one,just happen to stumble across the one from techpowerup that i posted
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Old August 18, 2008, 08:58 PM
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Quote:
Originally Posted by bojangles View Post
It is a weird thing indeed. I'm thinking that since right now they can't share the data between them, they process it by half the amount. Perhaps if they do enable, it will allow communication between the two GPUs and memory to allow faster processing. I don't understand why they wouldn't put in the PLX 2.0 chip if they're not going to use it...they could've saves a lot of money if they kept the same PLX chip in from the 3870X2. We'll see though because there's no word of a GX2 from Nvidia yet.
wow jangles you got some thoughts goin on there, i'm just wonderin how much a performance boost enabled xsp wil give
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Old August 19, 2008, 07:47 AM
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Well I'm thinking you could consider it as another "crossfire" like gateway on the card. I could see like a 20-30% increase, but I have no idea honestly. Those numbers could be high too, so don't take my word from it. I'm not a computer engingeer, I'm a power systems engineer lol...student, that is.
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