Okay, well It looks like I'll be adding 2 more HD4890-OC cards to my I7 next week, so now I have a question in general about bandwidth.

 

My I7 motherboard (Asus P6T, original, no WS no revoultion), runs the 3rd PCI-Express 16x slot at 4x if both of the other two slots run at 16x16x, so.. two questions arise from this.

 

1.) Does the ATI/AMD CrossFireX Bridge Connector provide additional communication bandwidth to the overall CrossFireX setup, enough to give performance above the 4x PCI-Express slot?

2.) Will I see a performance increase adding a 3rd card at 4x (even with the CrossFireX Bridge Connector) to my other two HD4890-OC cards in the first two 16x slots @ 16x speed (both of em)???

 

Additional Information about my system:

Motherboard: Asus P6T

Processor: Intel I7-920 (Overclocked @ 3800mhz)

Power Supply: CORSAIR Enthusiast Series TX950 (950 Watts, single-rail, 6 x 6+2 PCI-E power cables, 78 Amps on +12v) Link to power supply: http://www.newegg.com/Product/Product.aspx?Item=N82E16817139013

Memory:  Patriot Viper II Sector 7 Edition 24gb (6x4gb) @ 1814mhz, 10-11-11-30.  Link to ram: http://www.newegg.com/Product/Product.aspx?Item=N82E16820220497

Current video card: VisionTek Radeon HD 4890-OC (runs @ 950mhz core 1050mhz memory)

Using Antec Twelve Hundred V3 chassis.

Running Windows7 Ultimate x64

Edited: 12/09/2011 at 09:32 PM by kithylin

1) No.
2) Very little if any. I would advise against a third card.

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Regarding your response to 2.):  Are you saying that ATI CrossFireX does not scale well with a 3rd card in general? Or perhaps your comment is in regards to my 3rd slot being 4x speeded?

The auction I just won on ebay was for a pair of two HD4890 cards, So... I'm getting a 3rd one anyway.  My question is to use it, or sell it / keep it as a spare or something else if there's no point in using it.

Edited: 12/09/2011 at 09:37 PM by kithylin

 

Tri-Fire scaling works great, it's just that with the 3rd @x4 there may be little to no benefits of using the third card .. and some cards don't like to play nice in x4 slots either .. Best you can do, is to set them all up and see if you're happy with the results ..

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Alrighty.. Thank you for the answer.  Do you think my power supply is good enough to handle 3 of em? I mean, it looks like it's supposed to, It's just.. 3 is quite a bit of load to put on the thing and I've never tried to use more than 1 card with it before.

EDIT: Also it's not an X4 SIZED slot, the slot is the full 16x size, it's just Asus claims it runs at 4x SPEED, so...

Yea, it's common for manufacturers to put x16 size slots on the motherboard instead of x1, x4, and x8 sizes and only give them 4 or 8 electrical PCIe lanes. As for the PSU, it is strong enough, but like GG said that x4 slot is the problem, running a graphics card in anything but a x8 or x16 electrical slot, besides being a large bottleneck, can cause issues such as the card not being recognized and usable.

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Crosshair IV Formula, Phenom II x4 965 w/ Corsair H60, 8 GiB OCZ Platinum DDR3 1600, XFX HD 7970 Ghz, 512GB Vertex 4, 256GB Vector, 240GB Agility 3, Creative X-Fi Titanium w/ Creative Gigaworks S750, SeaSonic X750, HP ZR2440w, Win 7 Ultimate x64

 

Alrighty thanks for clearing all of this up guys and thanks for your time.  I may end up selling the third one later, I'll probably want to at least install it and see what it does first.  I only paid $88 with shipping for two 4890-overclocked cards.. might sell the other for $60 later, if it doesn't offer any performance increases.