For SLI, this means an NVIDIA chipset bearing the SLI sticker, although driver hacks sometimes coax other motherboards to work. Your motherboard also has to support the relevant technology. In either case, brands, clock frequencies, and memory sizes do not have to match however, mixing clock frequencies or memory sizes will drag down the superior card to match the inferior card. CrossFire is slightly more flexible, but cards can differ only in the last two digits of the model number and the suffix. For SLI, cards should be nearly identical they need to have the same model number, down to the 2- or 3-letter suffix. Fortunately, there's a compatibility chart. For CrossFire it used to mean having a CrossFire "Master" card (which cost extra), although some newer chipsets eliminate this requirement. For SLI this means explicit SLI support (usually with the special SLI connector) for each card. Your video cards must support SLI if made by NVIDIA, or CrossFire if made by ATI/AMD. But there are still some, and remeber that these are requirements and not recommendations. The requirements to build a system around these technologies have, fortunately, loosened up a bit over time. Requirements for an SLI or CrossFire system In practice these set-ups often perform terribly, and don't even touch a single, mid-range card of the same generation. As before, the possibility of selling the old card to finance a new one makes it hard to justify two cards on a cost basis.Īnd some people think it very clever to buy up two very cheap cards, stick them together, and have a cheap solution for great performance. Performance that is not too far above a mid-range card from the next generation. This yields performance comparable to a single high-end card from the same generation, typically. Others plan to buy a mid-range card, and down the line (once prices fall) add another mid-range card like it. But the two cards cost more overall (if you buy a card today and a next-gen card down the road, you can sell the first card to help finance the second one), consume more power (with rare exceptions), and generally not offer a performance advantage. Two of today's top-end cards put together will perform roughly as well as a high-end card from the next generation, assuming past trends hold. Combining multiple cards does provide more performance, but the gains are not huge and not universal. For them it is not such a clear proposition. If you absolutely must have the best performance that money can buy today, then these are technologies intended specifically for you. Tom's Hardware has performance benchmark charts that include single-, dual-, and quad-GPU configurations or just dual- and quad-GPU configurations. These issues remain when 3 or 4 GPUs are used, where again performance is nowhere near the theoretical limit. Additionally, there are sometimes driver issues with very new cards, which of course is very problematic for a technology aimed at early adopters. Typical performance gains are something like 20 to 50% above a single card. This means that under certain circumstances, with certain software, performance can actually be worse than a single card. Performance of SLI and CrossFire systems is heavily dependent on what is being rendered and on the video drivers. There are real-world issues related to parsing a scene out to the two cards, and some 3D engines are not very accomodating to the multi-card approach. ![]() However, in practice this is never achieved. The theoretical upper limit for performance of an SLI/CrossFire system with 2 GPUs is twice that of a single-card system (assuming two identical cards are used an issue we will touch on later). So do they provide twice (or three or four times) the performance of a single card? So computers with 2, 3, or 4 GPUs may be built using either technology. Because CrossFire allows different cards to be used, 3-GPU CrossFire systems (called CrossFireX, without the Quad) can be built by combining one card with 2 GPUs and another with 1 GPU. Additionally, NVIDIA has now made it possible to use 3 cards together (which it calls 3-way SLI). However, both companies have now produced cards with 2 GPUs on a single card (model numbers ending in X2), opening the door to what are called Quad-SLI or CrossFireX Quad configurations. Originally the limit was two cards, and therefore two Graphics Processing Units (GPUs). This is intended to be as transparent to the rest of the computer as possible. SLI and CrossFire provide a system for two or more video cards to work together to render the same video stream. Do I need an "SLI Certified"/"CrossFire Certified" power supply or memory?.Requirements for an SLI or CrossFire system.So do they provide twice (or three or four times) the performance of a single card?.
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