Explain SLI to me.

[Rich46yo]

I understand the basic concept. Two cards that do the work of one. I have a SLI MB with a GTX580 installed. Should I buy a 2nd 580, would it be worth it? And would the upgrade make more sense then buying a new single card. Exactly how would SLI work with modern games?

Thank you.

[Blagard]

Per your title I think reading wiki will explain a lot wiki SLI link

The rest of your questions seem more related to cost. I was under the impression a GTX580 is pretty good. So is increasing fps or detail worth anything to you if you can't actually tell the difference when playing a game? As different games put different loads on the graphics I think you need to be more specific about what you plan on playing. It seems to me that as a general rule the cost of cards at the top end goes up very steeply and so it is probably more a question of doing the maths. How does the performance/cost ratio compare. Again I think you need to check out tests for the games in question.

The single card vs two in SLI is interesting. Will a SLI setup actually give you a difference you can see? According to wiki it may even drop the performance on some applications but no specific games mentioned.

[Rich46yo]

According to wiki it may even drop the performance on some applications but no specific games mentioned.

Right, I know in certain games it wont make a difference but im wondering how it works out in the real world. Basically I want to keep this system current, able to play the new games at full steam, but dont necessarily want to buy the latest gaming card. Im sort of caught in the middle, with a good but older card, still good enough not to warrant spending $600 on a new one. I'd kinda like to buy a good used one as a cheaper alternative.

[BaldEagl]

Go to Tomshardware and check out the benchmark charts.  They bench every card alone and in SLI/Crossfire with several different applications/games.  See if a new card will bench higher than your card in SLI in the applications you use and if it will be cost effective.

[Debrody]

First, the GTX580 is still a very good card, i cannot imagine any game where it would struggle. A 3-monitor setup maybe.

Its all about how much is an other 580 nowadays. SLI will give you an about 50-70% performance gain in most of the newer games - a pair of 580s are about in par with, or a bit faster than the 680/770.

There are other eyepoints though. The 580 consumpts ~250 Watts. 2 of them can easily eat up to 500, even without OC-ed. With a suitable, decent CPU (i assume, you have at least an i7 9xx or an i5 2500), you might need an at least 750W PSU. Also, there is a chance that some games cannot take use of the SLI - then your setup will work as like it had one 580. Newer games usually have a decent CF/SLI support though, while the older ones just couldnt profit from the extra speed - 60fps limited by your monitor.

What i would advice:
-do you really need the extra power? Is there anything you cannot run well (maybe after some tweaking with the settings)?
-if your PSU is good enough, but you dont want to spend too much, doubling the 580s might worth it. But if your budget is high enough, i would go for a single card, at least a 770/780/7970GHz.

[Rich46yo]

Thanks for the advice. I only have a 750 watt power and that kinda concerns me. I just dont see 750 as enough, what with all the other stuff I have going as well.

[alskahawk]

 Here are some of my thoughts on SLI after having built a few for my use;  I am not familiar with the GTX 580. But in my opinion it is not worth adding a second cheap card to a system. I consider anything around 100$ or below to be a cheap card. $200 up medium to expensive. I don't think there is enough trade off of dollars to performance gained by adding a second cheap card to a system. Make sure your PSU can handle a second card. Newegg has a wattage calculator to check.

 Instead of two $100 cards. One $200 card is a better choice. But that's just my opinion. I have done cheap cards, medium and high end. It seems that your best gains are in the medium to upper end. I think it's probably due to the better stuff that comes with a better card. Again that's just an opinion.  
    

[Bino]

I only have experience with AMD's "crossfire" multi-card ability.  I had a single HD 5850 card in a machine with a first-generation i7 CPU, an i7-930 running a little bit faster than stock, at 3.4 GHz.  Adding a second 5850 video card improved in-game performance only slightly during very busy scenes.  The lowest number I saw with one card was down around 15 FPS, and with two, about 20 FPS.

YMMV

[MrRiplEy[H]]

I only have experience with AMD's "crossfire" multi-card ability.  I had a single HD 5850 card in a machine with a first-generation i7 CPU, an i7-930 running a little bit faster than stock, at 3.4 GHz.  Adding a second 5850 video card improved in-game performance only slightly during very busy scenes.  The lowest number I saw with one card was down around 15 FPS, and with two, about 20 FPS.

YMMV

AFAIK AH is not a supported Xfire/SLI game so you're not going to see big improvements if any. Without a proper profile only 1 card is utilized and the end result can even be slower than with a single card.

[Debrody]

AFAIK AH is not a supported Xfire/SLI game so you're not going to see big improvements if any. Without a proper profile only 1 card is utilized and the end result can even be slower than with a single card.

This. AH simply does not need 2 580s (i think), yet the newer, more demanding games usually can take use of the CF/SLI.

[guncrasher]

AFAIK AH is not a supported Xfire/SLI game so you're not going to see big improvements if any. Without a proper profile only 1 card is utilized and the end result can even be slower than with a single card.
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think ah has an sli  profile but its an older one.   i play with sli evga 465 and have full frames with everything on and shadow at 2048.  only problem i have had was this weekend with new clouds in tt when fps went into the 20s.
I play with 3 23in monitors at 52whateverx 1080p.



semp

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[Fulcrum]

This. AH simply does not need 2 580s (i think), yet the newer, more demanding games usually can take use of the CF/SLI.

That. depends.

SLI does improve frame rates and rendering even for games that don't support it fully.  Also, people who run games on a multi monitor setup (like me), and thus higher resolutions, are going to see a improvement as well.

[Gman]

I've been messing around with 680's and 780's in SLI this last year.  The SLI profile for AH2 isn't the best, and IMO I would recommend anyone who is focusing on AH graphics performance to not bother with SLI and get the fastest single GPU card they can afford.  The difference on a single 1080p 24" 144hz monitor or 3 of the same, with a single 680 4gb or in SLI is very  negligible, something SKuzzy warned/told me when I was buying my 2nd card to use for 3 screens.  He was absolutely correct, it didn't make much FPS improvement, if any.  With the 780gtx 3gb card being almost the equal as a Titan, as in 1 or 2 percent either way in most games, once you clock it a little higher with afterburner or whatever, for the price, it's far cheaper than 2 680's were when I purchased them, and faster as well, but, as I said, not much difference in AH fps wise, I see 144hz maxed out constantly on 1 screen or 3, until I turn up reflections/environment slider to max, then it'll drop a lot.

Unless you're really into BF3, or a bunch of other FPS/RTS/MM games that really use SLI and have a good profile, which you can google/check out easily, I wouldn't bother with SLI, as looking back, I wouldn't have for the limited boost I saw in many of the simulation games I play, or here with AH2.

[Fulcrum]

Your experience is somewhat different than mine, not only with AH2 (tho' admittedly its a small improvement) to other games such as ROF.

[Gman]

I don't play ROF.  Rome 2 for example sees zero increase with SLI right now, all of the DCS games see maybe 4 or 5 fps, if that.  In another thread I posted screen shots of all of this with both a 3820 and a 3930k @ 4.6, and with the Titan, 680gtx in sli and single.  I'll update it now with the 780's, but the difference is the same with AH2.  I will say with 3 screens running it makes a small difference having 2 680's instead of 1, but with the 780 it's not nearly as much - all of the cards will run 144fps which maxes out the monitors, again, so long as we aren't talking about reflections/environment. 

A few of the FPS games SLI makes a larger, much larger performance difference, but I wasn't talking about them.  BF3, CoD, the latest Far Cry, and the latest Crysis - yes, big big gains with SLI, running 2 780gtx compared to a single, or a single 680 or even the Titan on its own...HUGE performance gain.