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Old 04-07-08, 09:28 AM   #1
jcrox
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Default SLI FAQ

There have been so many threads with the same questions about SLI and so many wrong answers given to people that maybe a mod should sticky this.

To use SLI you need 2 cards with the same GPU i.e. 2 8800GTs, 2 7800GTXs, etc. They need to have the same amount of memory. There used to be a way to SLI 2 cards with different amounts of memory using RivaTuner or some tool of the sort but I'm not sure that's still possible.

The GPU's DO NOT need to be the same speed on both cards nor from the same vendor, just the same GPU. An EVGA 8800GT 512MB will work just fine with a BFG 8800GT OC card.

The memory DOES NOT need to be the same speed or same "timings" on both cards, just the same amount i.e both cards have 512MB. The memory is not "shared", if you have 2 cards with 512MB each you do not effectively have 1GB of video memory. Each card uses its own memory exclusively leaving you with an effective 512MB of video memory.

If one card has higher clocks than the other card it WILL NOT be automatically underclocked to match the speeds of the slower card. On every mother board I've tested this on it has worked that which ever card is in the primary pci-e slot (usually the top) the other cards clock speeds are set to match that cards speeds, so:
1. Higher clocked card in primary slot, slower card is automatically overclocked
2. Lower clocked card in primary slot, faster card is automatically underclocked
This applies to memory and GPU speeds, I haven't checked the shader clocks but I'm guessing they would sync up as well, maybe someone can verify this or I will when I get around to getting my 2nd 8800GT.
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Old 04-07-08, 09:34 AM   #2
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Thumbs up Re: SLI FAQ

Good post.
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Old 04-07-08, 11:00 AM   #3
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Default Re: SLI FAQ

Pretty good post for an old guy.
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Old 04-07-08, 02:18 PM   #4
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Default Re: SLI FAQ

Useful information here, thanks. One question tho... Can the cards be of different revisions? Like A2 and A3, i am getting an Evga KO AC3 version to use with my regular GTX.

Oh, and can i use different clocks for the two cards? Like the Evga card would probably OC better than my leaktek one.

One guy at XFX support claims that if you use two cards with different clocks the faster one will downclock to match the slower one:
http://forums.legitreviews.com/post7...7f64977#p73885

Witch am i supposed to believe?
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Old 04-07-08, 09:57 PM   #5
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Default Re: SLI FAQ

Quote:
Originally Posted by Soetdjuret
Useful information here, thanks. One question tho... Can the cards be of different revisions? Like A2 and A3, i am getting an Evga KO AC3 version to use with my regular GTX.

Oh, and can i use different clocks for the two cards? Like the Evga card would probably OC better than my leaktek one.
You wont be able to use different clocks, the speeds will automatically sync.

Quote:
One guy at XFX support claims that if you use two cards with different clocks the faster one will downclock to match the slower one:
http://forums.legitreviews.com/post7...7f64977#p73885

Witch am i supposed to believe?
I've heard tons of people say this and yet every motherboard I've tried it on it's depended on which slot you put which card in... may be it's been changed or maybe some motherboards are this way and others not....I have a friend with an EVGA 8800GT, I'll have to borrow it and double check this with newer boards but I know for sure this was how it worked with the EVGA, ABIT and ASUS NF4 motherboards I had and people said the same thing then.
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Old 04-07-08, 10:19 PM   #6
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Default Re: SLI FAQ

heh, I responded to that thread in the other forum and didn't even notice that its super old. From my experience the XFX support guy is wrong. Maybe there are some other people here that have differently clocked cards that can try it out.
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Old 07-18-08, 09:40 AM   #7
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Default Re: SLI FAQ

Sticky this! I was wondering about it
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Old 07-18-08, 10:22 AM   #8
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Default Re: SLI FAQ

Good info, stuck
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Old 07-18-08, 10:35 AM   #9
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Default Re: SLI FAQ

Good thread.
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Old 01-02-09, 08:11 AM   #10
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Default Re: SLI FAQ

Yupp
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Old 01-02-09, 09:06 AM   #11
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Default Re: SLI FAQ

http://www.slizone.com/page/slizone_faq.html
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