Hello everyoneI have seen many people making mistakes about MultiGPU technology or have difficulties understanding; therefore,I decided to write a guide that helps you understand it better.So,let's start!NVIDIA SLI is a platform that allows you to scale graphics performance by combining multiple NVIDIA graphics solutions in a single system.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.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.From Techreport.com:CrossFireX is, quite simply, an extension of the CrossFire dual-GPU feature to three and four GPUs.Here's the chart from AMD's website regarding which cards can you use in crossfire,motherboard support and more.3XXX to 5xxx Family5XXX to 7XXX FamilyR7 and R9 Family(Thanks for the link damric)Hybrid CrossFire allows integrated graphics and low-end discrete graphics to be used in CrossFire mode.Overall,both Hybrid CrossFire and Hybrid SLI are mainly for power savings and aren't a good solution for gaming and 3D performance(overall).Well , in general , the answer is NO;however,there are some methods(like driver hacks) that allows you to do this.Caution:There is no guarantee that this driver hacks work,so do it at your own risk!With the release of Core "i" CPUs,Intel announced chipsets(P55,X58,Z68,etc.) that allow users to use CrossFire and SLI on the same motherbard.(However,still some of them only support either SLI or CrossFire)But the newer chipsets like Z77,X79 etc. usually support both SLI and CrossFire.And it's safe the say the future models will be the same;supporting both SLI and CrossFire.For "Most" Nvidia cards the answer is yes,but there are some exceptions too,such as pairing a GTS 250 with a 9800GTX+,which can only be done if both cards have the same amount of memory. (It's possible because 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.)But for AMD/ATI cards,It's different.For older models like X1900 cards,you have to use the same/master card in order to run them in CrossFire mode.But for HD 2xxx cards and up,there are no master cards so you simply can use 2(or more) (same)cards in Crossfire.So the general answer is yes,with some exceptions.So it's recommended to use the same cards for best results.You can find more information regarding matching cards in SLI/Crossfire at the end of this guide.For Nvidia cards,the general answer is no."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 these cards in SLI,then the model,with higher amount of RAM,will reduce it's RAM to match the other card.For ATI cards,it's different.As an example,you can Crossfire HD 5870 2GB with it's 1GB version (but again the 2GB version lowers it's memory to 1GB)So,generally,,it's recommended to use 2(or more than 2) identical cards with the same amount of memory.Brands don't matter,as long as they're the same card with the same memory/speeds.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.Again,that's why I usually recommend using the same cards in multiGPU modes.It's been frequently asked whether to use 1 or 2 SLI/Crossfire bridges.The answer is that 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.3_With the release of the 10XX series from Nvidia both bridges can have a noticeable gain in performance. Nvidia now has what they call an HB SLI Bridge that uses both sets of contacts the card.Not always.There are some games that don't benefit from either SLI or CrossFire or require a patch in order to fully utilize both cards.For example,Flight simulator X doesn't benefit from either SLI or CrossFire;on the other hand,BattleField 4 benefits from this technologies.It depends on the game to be honest.This link has some great comparisons between single and multiGPU configurations in numerous gamesFor Crossfire and SLI certified boards, please check the motherboard makers website. It is a selling feature and will be listed.SLI certified motherboards:AMD recommended Motherboards:No,your computer's RAM isn't at all related to the cards you are using,just make sure it's compatible with the motherboard and CPU.For every configuration,the power requirement is different.Nvidia cards:AMD/ATI cards:There are some compatible models that aren't listed so always check with the manufacturers website at first.It all comes down to 2 factors:1)The games that you play2)The resolutions that you play atAs mentioned,there are some games that don't benefit from either SLI or Crossfire;also both SLI/Crossfire really shine when you play "at least on" 1080p,even on this resolution,a single powerful card can handle everything fine.It really depends on you.I "personally" prefer a single high-end card rather than 2 mid-range cards because usually,the single card produces less heat and has less power consumption but it may cost more too.So it all comes down to personal preference and budget.No.Adding another card with more memory doesn't double the overall memory of your cards.It again comes to personal preference and the games that you play.There are some specific games that scale better under SLI and vice-versa.For 2-way SLI,motherboards either support CrossFire at dual x16,dual x8 or x16x4 speeds.The first will give you the best performance.Dual x8 is also good and performs on par with dual x16 in most games.But x16x4 is kinda different.On PCI-E 1.0 boards/cards,there is a huge difference between x16x4 and dual x16(and 8x).On PCI-E 2.0/3,0 boards/cards;however,the performance gap isn't as high.(The performance is notable in some games though,especially on high resolutions)Generally, recommend dual x16 or dual x8 for MultiGPU setups.Here is a good article which compares CrossFire performance between dual x16,dual x8 and x16x4List of NVIDIA and AMD/ATI MultiGPU compatible Graphic Cards: (All of them are PCI-EXPRESS cards,AGP cards don't support any kind of multiGPU setups)NVIDIA cards(Desktop models)Geforce TITAN Family:NVIDIA GEFORCE GTX TITAN XpNVIDIA GEFORCE GTX TITAN X PascalNVIDIA GEFORCE GTX TITAN XNVIDIA GEFORCE GTX TITAN ZNVIDIA GEFORCE GTX TITAN BLACKNVIDIA GEFORCE GTX TITANGeforce RTX 20 - NVLink (SLI-Ready)NVIDIA GeForce RTX 2080NVIDIA GeForce RTX 2080tiGeforce GTX 10 Family:NVIDIA GeForce GTX 1080tiNVIDIA GeForce GTX 1080NVIDIA GeForce GTX 1070Geforce GTX 900 Family:NVIDIA GeForce GTX 980tiNVIDIA GeForce GTX 980NVIDIA GeForce GTX 970NVIDIA GeForce GTX 960Geforce GTX 700 Family:NVIDIA GEFORCE GTX 780TiNVIDIA GEFORCE GTX 780NVIDIA GEFORCE GTX 770NVIDIA GEFORCE GTX 760Geforce GTX 600 Family:NVIDIA GEFORCE GTX 680NVIDIA GEFORCE GTX 670NVIDIA GEFORCE GTX 660NVIDIA GEFORCE GTX 660tiNVIDIA GEFORCE GTX 650ti BOOST (must be the boost model, normal 650/650ti's are NOT SLI ready)Geforce GTX 500 Family:NVIDIA GEFORCE GTX 590(1 PCB*)NVIDIA GEFORCE GTX 580NVIDIA GEFORCE GTX 570NVIDIA GEFORCE GTX 560TiNVIDIA GEFORCE GTX 560NVIDIA GEFORCE GTX 550TiNVIDIA GeForce GT 545 DDR3Geforce 400 Family:NVIDIA GEFORCE GTX 480NVIDIA GEFORCE GTX 470NVIDIA GEFORCE GTX 465NVIDIA GEFORCE GTX 460NVIDIA GEFORCE GTS 450Geforce 200 Family:NVIDIA GEFORCE GTX 295NVIDIA GEFORCE GTX 285NVIDIA GEFORCE GTX 280NVIDIA GEFORCE GTX 275NVIDIA GEFORCE GTX 260 Core 216(You can pair it with the Core 192 version.)NVIDIA GEFORCE GTX 260 Core 192NVIDIA GEFORCE GTX 250(You can pair it with 9800GTX+ in SLI configuration,however make sure that both cards have the same amount of memory)Geforce 100 Family:GeForce GTS 150GeForce GT 130GeForce GT 120Geforce 9 Family:NVIDIA GEFORCE 9800GX2 (2 PCB's)NVIDIA GEFORCE 9800GTX+(You can pair it with a Nvidia 9800GTX in SLI configuration,but it's recommended to use the 9800GTX+ card in the first PCI-E 16x slot.)NVIDIA GEFORCE 9800GTXNVIDIA GEFORCE 9800GTNVIDIA GEFORCE 9600GTNVIDIA GEFORCE 9600GSONVIDIA GEFORCE 9500GTNVIDIA GEFORCE 9400GTGeforce 8 Family:NVIDIA GEFORCE 8800ULTRANVIDIA GEFORCE 8800GTXNVIDIA GEFORCE 8800GTS 512NVIDIA GEFORCE 8800GTNVIDIA GEFORCE 8800GTS 640NVIDIA GEFORCE 8800GTS 320NVIDIA GEFORCE 8800GSNVIDIA GEFORCE 8600GTSNVIDIA GEFORCE 8600GTNVIDIA GEFORCE 8500GTNVIDIA GEFORCE 8400GSGeforce 7 Family:NVIDIA GEFORCE 7950GX2 (2 PCB's)NVIDIA GEFORCE 7900GTXNVIDIA GEFORCE 7950GTNVIDIA GEFORCE 7900GTNVIDIA GEFORCE 7900GSNVIDIA GEFORCE 7800GTX 512NVIDIA GEFORCE 7800GTX 256NVIDIA GEFORCE 7800GTNVIDIA GEFORCE 7600GTNVIDIA GEFORCE 7600GSNVIDIA GEFORCE 7300GTNVIDIA GEFORCE 7300GSNVIDIA GEFORCE 7300LEGeforce 6 Family:NVIDIA GEFORCE 6800ULTRANVIDIA GEFORCE 6800GTNVIDIA GEFORCE 6800GSNVIDIA GEFORCE 6800NVIDIA GEFORCE 6800LENVIDIA GEFORCE 6600GTNVIDIA GEFORCE 6600NVIDIA GEFORCE 6600LENVIDIA cards(Notebook models)Geforce 900M Family:GeForce GTX 980MGeForce GTX 970MGeForce GTX 965MGeforce 800M Family:NVIDIA GEFORCE GTX 880MNVIDIA GEFORCE GTX 870MNVIDIA GEFORCE GTX 860MGeforce 700M Family:NVIDIA GEFORCE GTX 780MNVIDIA GEFORCE GTX 770MNVIDIA GEFORCE GTX 765MNVIDIA GEFORCE GTX 760MNVIDIA GEFORCE GTX 750MGeforce 600M and MX Family:GeForce GTX 680MXGeForce GTX 660MGeForce GTX 670MXGeForce GTX 675MXGeForce GTX 670MGeForce GTX 675MGeforce 500M Family:NVIDIA GEFORCE GTX 580MNVIDIA GEFORCE GTX 570MNVIDIA GEFORCE GTX 560MGeforce 400M Family:NVIDIA GEFORCE GTX 485MNVIDIA GEFORCE GTX 480MNVIDIA GEFORCE GTX 470MNVIDIA GEFORCE GTX 460MGeforce 200M Family:NVIDIA GEFORCE GTX 280MNVIDIA GEFORCE GTX 260MGeforce 100M series:NVIDIA GEFORCE GTS 160MNVIDIA GEFORCE GTS 150MNVIDIA GEFORCE GTS 130MGeforce 9 Family:NVIDIA GEFORCE 9800MGTXNVIDIA GEFORCE 9800MGTNVIDIA GEFORCE 9800MGTSGeforce 8 Family:NVIDIA GEFORCE 8800MGTXNVIDIA GEFORCE 8700MGTNVIDIA GEFORCE 8600MGTGeforce 7 Family:NVIDIA GEFORCE 7950GTXNVIDIA GEFORCE 7900GTXNVIDIA GEFORCE 7800GTXAMD cards(Desktop models)AMD Radeon RX Family:AMD RX 580AMD RX 570AMD RX 560AMD RX 540(OEM)AMD RX 480AMD RX 470AMD RX 460AMD Radeon R9 Family:AMD R9 295X2AMD R9 290XAMD R9 290AMD R9 280XAMD R9 280AMD R9 270XAMD R9 270AMD Radeon R7 Family:AMD R7 265AMD R7 260XAMD R7 260AMD R7 250XAMD R7 250AMD R7 240AMD HD 7xxx Family:AMD HD 7970AMDI HD 7950AMD HD 7870AMD HD 7850AMD HD 7770AMD HD 7750AMD HD 6xxx Family:AMD HD 6990(1 PCB)AMD HD 6970AMD HD 6950AMD HD 6870AMD HD 6850AMD HD 6670AMD HD 6570AMD HD 5xxx Family:AMD HD 5970AMD HD 5870 Eyefinity 6 edition(Can be used in CrossFire with the non-Eyefinity 6 version)AMD HD 5870AMD HD 5850AMD HD 5830AMD HD 5770AMD HD 5750AMD HD 5670AMD HD 5570AMD HD 5550AMD HD 5450AMD HD 4xxx Family:AMD HD 4890AMD HD 4870X2(1 PCB)AMD HD 4870AMD HD 4850AMD HD 4830AMD HD 4770AMD HD 4750AMD HD 4670AMD HD 4650AMD HD 4550AMD HD 4350AMDHD 3xxx Family:AMD HD 3870X2(Read the extra information about HD 5970,its the same for HD 3870X2)AMD HD3870AMD HD 3850AMD HD 3830AMD HD 3650AMD HD 3470AMD HD 3450AMD HD 2xxx Family:AMD HD 2900XTAMD HD 2900PROAMD HD 2900GTAMD HD 2600XTAMD HD 2600 PROAMD HD 2400XTAMD HD 2400 PROAMD X19xx Family:AMD X1950XTXAMD X1950PROAMD X1900XTXAMD X1900XTAMD X1900GT(Unlike X1900XT and 1900XTX which require a Master card to run in CrossFire,this card can be paired with another X1900GT card)AMD X1xxx Family:AMD X1800XTAMD X1800GTOAMD X1800XLAMD X1650 PROAMD X1650XTAMD X1600XTAMD X1600PROAMD X1550AMD X1300XTAMD X1300PROAMD X1300AMD X850 Family:AMD X850XT-PEAMD X850XTAMD X850 PROAMD Cards(Notebook models). Out of date.AMD HD 6xxx Family:AMD HD 6970MAMD HD 5xx Family:AMD HD 5870MAMD HD 4xxx Family:AMD HD 4870MAMD HD 3xxx Family:AMD HD 3870M* PCB stands for Printed Circuit Board, its the hard "plastic-like" colored part in a graphics card/motherboard.So,I hope reading this guide helps you understand MultiGPU technology better.I've kept this topic opened so that you can ask your questions and post your suggestions about the it.Special thanks to emp,4745454b,alias_the_?jester and MouseMonkey and NukeMaster for helping making this guide.