http://www.tomshardware.com/forum/245454-33-crossfire-faqs

Hello all I have seen many users making mistakes about multiGPU technology or have problems understanding it,therefore i decided to write a guide that helps you understand this technology better , so lets start.

 

What is SLI ? NVIDIA SLI is a platform that allows you to scale graphics performance by combining multiple NVIDIA graphics solutions in a single system.

 

What is Nvidia Hybrid SLI?I found a very good information from Hothardware.com :NVIDIA's Hybrid SLI technology gives users the ability to pair an IGP, or mGPU (motherboard GPU), with a discreet graphics card, or cards, for two new modes of operation. NVIDIA calls these new modes Hybrid Power and GeForce Boost.GeForce Boost does what its name suggests. By coupling the motherboard's integrated GPU with a discreet graphics card, the 3D rendering workload is shared between the two GPUs for a boost in performance. Currently, GeForce Boost is only supported by GeForce 8400 GS and 8500 GT discreet cards, as for the IGP, only the next-gen nForce 700a series of chipsets due to arrive this quarter will be supported initially.

 

What is CrossFire ?CrossFire is a high-performance PC Gaming Platform technology that enables multiple ATI Radeon graphics cards and a CrossFire-ready motherboard in a single computer to increase graphics quality and performance.

 

What is CrossFireX(Quad CrossFire)?I found a very good definition for it in techreport.com:CrossFireX is, quite simply, an extension of the CrossFire dual-GPU feature to three and four GPUs.

Here is a good chart about the cards and motherboards which support CrossFire,CrossFireX and the compatibility list:

 

What is AMD Hybrid CrossFire?Its a technology from AMD which allows an integrated graphics and low-end discrete graphics in CrossFire mode.You are basically taking two very slow GPUs and making one not-so-slow GPU.This can only be done with AMD chipsets and AMD/ATI Graphics.

 

Lets simply say that both Hybrid CrossFire and Hybrid SLI are mainly for power savings and won't give users a great performance boost games or intensive 3D applications.

 

Can you use SLI on a CrossFire board or can you use CrossFire on a SLI board ?Well , in general , the answer is NO. But it's said that if you hack the drivers , you can use SLI on a CrossFire board or CrossFire on a SLI board.Caution:There is no guarantee that if you hack the drivers then you use SLI on a CrossFire Motherboard or CrossFire on a SLI board, so do it at your own risk!

 

However,with the release of i7/i5,Intel announced two chipsets which are X58 and P55 that allow users to use CrossFire and SLI on the same motherbard.(However X58/P55 boards support only CrossFire,some only support SLI and some support both,so if you wanted to buy a new motherboard,make sure you check this first.

 

Do the cards have to be same model?For "Most" Nvidia cards the answer is yes,but there are some exceptions too like pairing a GTS 250 with a 9800GTX+,which can be done if both cards have the same amount of memory since the GTS 250 is actually a re-badged 9800GTX+ but again there are some cards like 9800GT and 8800GT which have the same specifications but in general you can't pair them in SLI,some users have reported that by flashing a 8800GT's BIOS to a 9800GT's BIOS,you can do it,but its risky and not recommended.I wrote about the cards which have different names but can be used in SLI mode in the "Model's section" down this post,other than those all other cards must be same model in order to run in SLI mode.but about AMD/ATI models,for models like X1900 series and lower you have to use the same/master card to use CrossFire but for HD 2xxx series and up,check the compatibility chart on top of this post.For Nvidia cards,here is an example:You have a NVIDIA Geforce 7800GTX , and you want to add another card , the second card has to be 7800GTX exactly.

 

But what about the memory? Can you SLI 7800GTX 256MB with it's 512MB version ? For Nvidia cards,the general answer is no.Here is from SLI zone:http://www.slizone.com/object/slizone_ask_mmm013.html"Another misconception is that the GeForce 7800 GTX (256MB) graphics cards and the GeForce 78000 GTX 512 graphics cards can be paired together. Since these graphics cards use different GPUs, they unfortunately CAN'T be paired together. Always refer the Learn More or Build sections of SLIZone." So,you generally can't pair a 7800GTX 256 with 7800GTX 512 or GTX 460 768MB with its 1GB version unless you use some 3rd party applications(which isn't recommended).However,if you manage to run them in SLI,(for example a 7800GTX 256 with 7800GTX 512)the second card will lower its memory to 256MB in order to match it with the other card.So the performance will be the same as 2 7800GTX 256s.

On the other hand,there are some few exceptions too.For example Nvidia GTS 250 can be paired with Nvidia 9800GTX+ if they have the same memory.

 

But for ATI cards,it's different.As an example,you can Crossfire HD 5870 2GB with it's 1GB version but the 2GB version lowers it's memory to 1GB,so you'll get the performance of 2 5870's with 1GB RAM.

 

What about brands ? Well the brand doesn't matter , again for example , you can use a XFX card with a EVGA card , or a SAPPHIRE card with a DIAMOND card , just make sure they have the same memory and same clocks.

 

What happens if the cards have different amount of speed?For ATI cards;One of the cards will raise/lower its clock speeds to reach the other card's speeds.For Nvidia cards;Well it "was" like ATI with older drivers, but with new drivers its quite different.If you use 2(or more) Nvidia cards with different clock speeds in SLI mode,none of them will change their clocks and they will perform at their default clock speed.

 

A Very important note about CrossFire:Many users ask to use 1 brige or 2 briges when they want to use 2 cards in CrossFire mode.The answer is it will work with 1 bridge without any problems but i recommend using both bridges because:1_You will never lose either of these bridges.2_Some users have reported a minimal(Not noticeable) performance increase.

 

Do SLI or CrossFire always improve performance ?Not Always , there are some games that dont take advantage of SLI or CrossFire , so you wont see a difference between 2 cards and 1 card in those games , but in games that take advantage of SLI or CrossFire , 2 cards will perform better than one.

 

What are SLI and CrossFire certified Motherboards?For SLI certified Motherboards ,go here :http://www.slizone.com/object/slizone_build_mobo.htmlFor CrossFire certified Motherboards check here:http://ati.amd.com/technology/cros [...] rown1.html

 

WARNING;Some RAMs have SLI or CrossFire logo on them. Many people ask if they are the only RAMs which support SLI or Crossfire.

Well thats wrong,there are many RAMs which dont have SLI or CrossFire logo but you can use SLI or CrossFire with them without any problem.

 

What are the power requirements for SLI or CrossFire ?For each card , the Power requirement is different , if you want to know if your Power Supply can handle SLI or CrossFire , check here For NVIDIA cards, go here:http://www.slizone.com/object/slizone_build_psu.html WARNING;There are some Power Supplies which aren't in the List , but they are compatible , you have to check the manufactures sites too.And for CrossFire, check here :http://sites.amd.com/us/game/produ [...] plies.aspx

 

Is it really necessary to use SLI or CrossFire ?Well , it really depends mostly on the resolutions and games you play , resolutions like 1920x1200 and higher benefit more from SLI or CrossFire than resolutions like 1600x1200 or lower (I don't mean SLI or CrossFire won't be good for resolutions like 1600x1200 or lower , i am just saying that SLI or CrossFire shines in higher resolutions.)This(MultiGPU technology) has been more optimized though and has become more mature than before, i mean in the first years of MiltiGPU technology the drivers werent as good as they are now and also not all games took advantage from MultiGPU, but things have gotten better(but not the best, because there are still games that don't take advantage MultiGPU like Flight Simluator X and there are still lots of driver problems too.)So in some of today games that really drain a lot of power from GPU, MultiGPU performs good at low resolutions (again in some games).Also as i said , it depends on what games (with what settings) you play , for example if you just want to play games at good settings (with not everything at maximum settings) then MultiGPU technology isn't needed , but if you want to play with every option at maximum settings with a high resolution, then either SLI or CrossFire would help.Caution: Due to some problems (like Drivers and etc) in some games, a single card (like X1900XT) may beat 2 1900XT in CrossFire mode! so don't always think that 2 cards will beat one card.

 

Some games like FLIGHT SIMULATOR X are mostly CPU-limited rather than GPU-limited:http://www23.tomshardware.com/grap [...] &chart=293

 

8800GTX VS 8800GTX in SLI :

 

8800GTX:1920x1200 : 22.6 1600x1200 : 22.4 1280x1024 : 23.0

8800GTX in SLI:1920x1200 : 22.6

1600x1200 : 22.4 1280x1024 : 23.0

 

But here is an example of a game which benefits from SLI like OBLIVION:

 

8800GTX VS 8800GTX in SLI :

 

8800GTX:1920x1200 : 28.71600x1200 : 32.51280x1024 : 43.6

 

8800GTX in SLI:1920x1200 : 53.81600x1200 : 61.21280x1024 : 77.1

 

So is it better to get 2 mid-range cards or 1 high-end card?I answer this with an example,lets say we want to compare 2 AMD/ATI HD 4770's with 1 AMD/ATI HD 4870,well in games that benefit from MultiGPU,2 HD 4770's would win but there are some exceptions too,for example some games doesn't benefit from MultiGPU(Which i talked about this)and in those situations the faster card takes the lead.Also many ask that whether to get 2 HD 4870's in CrossFire or 1 HD 4870X2(I mean getting 2 cards and use them in CrossFire/SLI or get a single card which has the power of 2 cards)Well by looking at the benchmarks you will find out that actually 1 HD 4870X2 is faster than 2 HD 4870's by 0-15% in "MOST" games(there are some exceptions too that 2 HD 4870's take the lead)also 1 HD 4870X2 doesn't need a MultiGPU Capable motherboard and it produces less heat and has lower power consumption too.

 

Do SLI or CrossFire double the memory ?This is one the questions that many people make mistake understanding it .The answer is NO , SLI or CrossFire doesnt double the memory , You have a 512MB card , adding another card wont make your memory 1GB, it still will be 512MB,so both cards will use 512MB of RAMs but the memory won't double.Another example :A game needs 512MB card to run at maximum settings , and you have a 256MB card , and you think if you add another 256MB card , your memory will be 512MB and thats not true.

 

You may see this mistake in many sites.

 

Which is better , SLI or CrossFire ?Well , you cant say exactly which is better , in some games SLI does better than CrossFire and in some games CorssFire does better than SLI, for benchmarks and tests,check Tom'shardware VGA chartshttp://www.tomshardware.com/charts [...] rds,1.html

 

A note about MotherboardsSome Motherboards support Multi-GPU Technology at Dual x16 mode, some support it at Dual x8 mode and some support it at x16x4 mode Etc, what are the differences?Well for getting the best performance out of Multi-GPU cards,you need a Motherboard that supports Multi-GPU at dual(Or more) 16x mode like Nvidia 790i ULTRA SLI, Nvidia790i SLI, Nvidia 780i SLI, Nvidia 680i( As i said, NVIDIA 790i ULTRA SLI ,790i SLI ,780i SLI and 680i SLI support 3-Way SLI too(Nvidia 680i LT SLI chipset has 2 PCI-E 16x slot which supports 2-way SLI only.),Nvidia 590i SLI, Nvidia nForce4 SLI 16x, ATI CrossFire Xpress 3200,Intel X38,X48 and X58.

 

Dual 8x is a very good configuration too,it doesn't have alot of difference(performance wise) with Dual 16x and its cheaper too.Chipests like Intel P55*,Intel P45 Nvidia 750i SLI, Nvidia 650i SLI,NVIDIA 570i SLI, NVIDIA nForce4 SLI, ATI Radeon Xpress 200, Intel 975x and ONLY few Intel P35 boards(Like Asus BLITZ FORMULA and ASUS BLITZ EXTREME) support Multi-GPU at dual x8 mode.

 

However,there are some expections too,for example EVGA has a 750i Motherboard(The model of it isEVGA 750i SLI FTW)Which supports SLI at dual x16 mode unlike many 750i Motherboards which support SLI at dual x8 mode.

 

The last one is x16x4, this one is the weakest and doesn't perform very good compared to dual x8 or dual x16,so i won't recommend it for Multi-GPU configuration. Intel P35 and P965 chipsets support Multi-GPU at x16x4 mode.However,the statement above is true with PCI-E 1.0 cards,because PCI-E 2.0 cards are different.And if you use 2(or more) PCI-E 2.0 cards in multiGPU mode and at x16x4 speed,they will perform close to dual x8/x16 mode.

 

Here is a good review which compares CrossFire performance between dual x16,dual x8 and x16x4http://www.tomshardware.com/review [...] ,2095.html

 

List of NVIDIA and AMD/ATI MultiGPU compatible Graphic Cards: (All of them are PCI-EXPRESS cards,MutliGPU technology is for PCI-EXPRESS cards not for APG cards.)

 

NVIDIA cards(Desktop models)Geforce GTX 500 Family:NVIDIA GEFORCE GTX 590(2 cards on a Single PCB)

NVIDIA GEFORCE GTX 580(Supports 3-Way SLI too)NVIDIA GEFORCE GTX 570(Supprts 3-way SLI too)NVIDIA GEFORCE GTX 560TiNVIDIA GEFORCE GTX 550TiNVIDIA GEFORCE GT 520

 

Geforce 400 Family:NVIDIA GEFORCE GTX 480(Supports 3-Way and 4-Way SLI too)NVIDIA GEFORCE GTX 470(Supports 3-Way and 4-Way SLI too)NVIDIA GEFORCE GTX 465NVIDIA GEFORCE GTX 460NVIDIA GEFORCE GTS 450NVIDIA GEFORCE GT 440NVIDIA GEFORCE GT 430

 

Geforce 200 Family:NVIDIA GEFORCE GTX 295NVIDIA GEFORCE GTX 285(Supports 3-Way SLI too)NVIDIA GEFORCE GTX 280 (Supports 3-Way SLI too)NVIDIA GEFORCE GTX 275(Supports 3-Way SLI too)NVIDIA GEFORCE GTX 260 Core 216(Supports 3-Way SLI too and also you can pair this card with a NVIDIA GEFORCE GTX 260 Core 192 in SLI configuration.)NVIDIA GEFORCE GTX 260 Core 192 (Supports 3-Way SLI too)NVIDIA GEFORCE GTX 250(Supports 3-Way SLI too and also you can pair this card with a 9800GTX+ in SLI configuration,however make sure that both cards have the same amount of memory)

 

Geforce 9 Family:NVIDIA GEFORCE 9800GX2NVIDIA GEFORCE 9800GTX+(Supports 3-Way SLI too and also you can pair this card with a Nvidia 9800GTX in SLI configuration,but its recommended to use the 9800GTX+ card in the first PCI-E 16x slot.)NVIDIA GEFORCE 9800GTX(Supports 3-Way SLI too)NVIDIA GEFORCE 9800GTNVIDIA GEFORCE 9600GTNVIDIA GEFORCE 9600GSONVIDIA GEFORCE 9500GTNVIDIA GEFORCE 9400GT

 

Geforce 8 Family:NVIDIA GEFORCE 8800ULTRA (Supports 3-Way SLI too)NVIDIA GEFORCE 8800GTX (Supports 3-Way SLI too)NVIDIA GEFORCE 8800GTS 512NVIDIA GEFORCE 8800GTNVIDIA GEFORCE 8800GTS 640NVIDIA GEFORCE 8800GTS 320NVIDIA GEFORCE 8800GS

NVIDIA GEFORCE 8600GTSNVIDIA GEFORCE 8600GTNVIDIA GEFORCE 8500GTNVIDIA GEFORCE 8400GS

 

Geforce 7 Family:NVIDIA GEFORCE 7950GX2(Remember, you may think that because 7950GX2 is actually "2 cards attached to one" then you need a SLI motherboard to use it, but you dont, for single 7950GX2, you need just one PCI-E 16x slot.)NVIDIA GEFORCE 7900GTXNVIDIA GEFORCE 7950GT NVIDIA GEFORCE 7900GT NVIDIA GEFORCE 7900GS NVIDIA GEFORCE 7800GTX 512NVIDIA GEFORCE 7800GTX 256NVIDIA GEFORCE 7800GT NVIDIA GEFORCE 7600GTNVIDIA GEFORCE 7600GSNVIDIA GEFORCE 7300GTNVIDIA GEFORCE 7300GSNVIDIA GEFORCE 7300LE

 

Geforce 6 Family:NVIDIA GEFORCE 6800ULTRANVIDIA GEFORCE 6800GTNVIDIA GEFORCE 6800GSNVIDIA GEFORCE 6800NVIDIA GEFORCE 6800LENVIDIA GEFORCE 6600GTNVIDIA GEFORCE 6600NVIDIA GEFORCE 6600LE

  

NVIDIA cards(Notebook models)

  

Geforce 400M Family:NVIDIA GEFORCE GTX 485MNVIDIA GEFORCE GTX 480MNVIDIA GEFORCE GTX 470MNVIDIA GEFORCE GTX 460M

  

Geforce 200M Family:NVIDIA GEFORCE GTX 280MNVIDIA GEFORCE GTX 260M

 

Geforce 100M series:NVIDIA GEFORCE GTS 160MNVIDIA GEFORCE GTS 150MNVIDIA GEFORCE GTS 130M

 

Geforce 9 Family:NVIDIA GEFORCE 9800MGTXNVIDIA GEFORCE 9800MGTNVIDIA GEFORCE 9800MGTS

 

Geforce 8 Family:NVIDIA GEFORCE 8800MGTXNVIDIA GEFORCE 8700MGTNVIDIA GEFORCE 8600MGT

 

Geforce 7 Family:NVIDIA GEFORCE 7950GTXNVIDIA GEFORCE 7900GTXNVIDIA GEFORCE 7800GTX

 

AMD/ATI cards(Desktop models)

 

AMD/ATI HD 6xxx Family:AMD/ATI HD 6990(2 cards on a single PCB)AMD/ATI HD 6970AMD/ATI HD 6950AMD/ATI HD 6870AMD/ATI HD 6850AMD/ATI HD 6670AMD/ATI HD 6570

 

AMD/ATI HD 5xxx Family:AMD/ATI HD 5970(Warning:The HD 5970 is NOT 2 cards (like Nvidia 9800GX2).Its actually 2 GPUs on one card and it has 1 PCB** compared to 2 PCBs of 9800GX2,so you "Don't" need a CrossFire board to use this card,it requires only one slot.)AMD/ATI HD 5870 Eyefinity 6 edition(Can be used in CrossFire with the non-Eyefinity 6 version)AMD/ATI HD 5870AMD/ATI HD 5850

AMD/ATI HD 5830AMD/ATI HD 5770AMD/ATI HD 5750AMD/ATI HD 5670AMD/ATI HD 5570AMD/ATI HD 5550AMD/ATI HD 5450

 

AMD/ATI HD 4xxx Family:AMD/ATI HD 4890AMD/ATI HD 4870X2(Read the extra information about HD 5970,its the same for HD 4870X2)AMD/ATI HD 4870AMD/ATI HD 4850AMD/ATI HD 4830AMD/ATI HD 4770AMD/ATI HD 4750AMD/ATI HD 4670AMD/ATI HD 4650AMD/ATI HD 4550AMD/ATI HD 4350

 

AMD/ATI HD 3xxx Family:AMD/ATI HD 3870X2(Read the extra information about HD 5970,its the same for HD 3870X2)AMD/ATI HD3870AMD/ATI HD 3850AMD/ATI HD 3830AMD/ATI HD 3650AMD/ATI HD 3470AMD/AT HD 3450

 

AMD/ATI HD 2xxx Family:AMD/ATI HD 2900XTAMD/ATI HD 2900PROAMD/ATI HD 2900GTAMD/ATI HD 2600XTAMD/ATI HD 2600 PROAMD/ATI HD 2400XTAMD/ATI HD 2400 PRO

 

AMD/ATI X19xx Family:AMD/ATI X1950XTXAMD/ATI X1950PROAMD/ATI X1900XTXAMD/ATI X1900XT

AMD/ATI X1900GT(Unlike X1900XT and 1900XTX which require a Master card to run in CrossFire,this card can be paired with another X1900GT)

 

AMD/ATI X1xxx Family:AMD/ATI X1800XTAMD/ATI X1800GTOAMD/ATI X1800XLAMD/ATI X1650 PROAMD/ATI X1650XTAMD/ATI X1600XTAMD/ATI X1600PROAMD/ATI X1550AMD/ATI X1300XTAMD/ATI X1300PROAMD/ATI X1300

 

AMD/ATI X850 Family:AMD/ATI X850XT-PEAMD/ATI X850XTAMD/ATI X850 PRO

  

AMD/ATI Cards(Notebook models)

 

AMD/ATI HD Family

 

AMD/ATI HH 6xxx Family:AMD/ATI HD 6970M

 

AMD/ATI HD 5xx Family:AMD/ATI HD 5870M

 

AMD/ATI HD 4xxx Family:AMD/ATI HD 4870M

 

AMD/ATI HD 3xxx Family:AMD/ATI HD 3870M

 

*:Most of Intel P55 chipset motherboards support CrossFire at dual x8 mode but there are some exceptions too which support CrossFire at x16x4 mode.http://www.intel.com/products/desk [...] erview.htm

 

PCI Express 2.0 interface :Offers up to 2.5GT/s for fast access to peripheral devices and networking with up to 8 PCI Express* 2.0 x1 ports, configurable as x2 and x4 depending on motherboard designs.

 

**: emp and 4745454b (They are good friends of mine in this forum who helped me very much)gave me a good definition and explanation of PCB to me: PCB stands for Printed Circuit Board, its the hard "plastic-like" colored part in a graphics card/motherboard.

 

9800GX2 has 2 PCBs so its actually 2 cards attached to one.But HD 3870X2 has 1 PCB and its actually 2 GPUs on card which has the power of 2 HD 3870s.

 

Warning; AMD/ATI X1800/X1900/X1950 cards need a CrossFire-Edition of them to run in CrossFire mode.But for HD Family its different, they don't need CrossFire-Edition, they just cant work with each other for example a HD 2600 works with another HD 2600 just fine.Also please read the note about CrossFireX at the first parts of this guide.

 

If you found something wrong in this guide please tell me to fix it,also i thank all who helped me in this topic.Also if you have seen that i have put a link from other site,its because that it had a very good information about MULTI-GPU technology.

 

So i hope reading this guide will help you understand MultiGPU technology better.