Steve Smith explains why Quad SLI is not 4-way SLI, but 2-Way SLI with more GPUs.
Episode #5-37 released on June 3, 2015
Talking about the true number of PCI-E lanes is bound to spark some debate. Many count the number of available lanes on mainboards, add them all up and presume that is the real number. Some seek out resources like Intel's Ark for more precision information. The reasoning is usually a debate on how many graphics cards we can put into SLI in a given system. There is another issue, many boards are capable of Quad SLI. Because of those claims, many believe those same boards can achieve 4-way SLI, which is not true. Today, I clarify the difference once and for all.
First, most Quad SLI enabled boards only have two slots long enough for two graphics cards. This being at least one X16, and an X8 PCI-E slot. The rest of the slots are usually PCI-E X1, or X4 slots. Sometimes one or two slots can be PCI, and not PCI-E. This alone should indicate the fact that the graphics card support is, in theory, limited to 2-way SLI.
However, the boards do clearly state that they support Quad SLI, what is going on?
Well, the answer is going to be simple. While AMD's Crossfire will support up to 4 cards, without an issue, NVidia requires a minimum of 8 available PCI-E lanes per graphics card, which intends to be put into SLI mode. Most current consumer processors only have 16 PCI-E lanes, so mathematically speaking, it limits us to two distinct cards.
For those who do not know this, the numbers on an NVidia GTX GeForce card mean something. Ignoring the first digit, which we could call the generation, even if that is wrong, the last two digits can range from 10 to 90. Normally, an average gaming graphics card from NVidia will have a rating number ending with 60, which is capable of playing most games without any issues. Then we got the 70 and 80 lines which are better. Cards ending in 10 to 80, also, have a common characteristic, they have a single GPU on the PCB. NVidia graphics cards ending in 90 have two GPUs on the PCB.
Now, most of you would technically agree, two GPUs are better than one, except for many issues that come with it. Power, and heat are some of the issues, and let's not forget drivers. A dual GPU NVidia card, technically, already has built in SLI, and this is only useful if game developers support those cards. Having two 90 cards would give you a 2-way, dual GPU, SLI, however, these are not common for a really good set of reasons. And those are what are referred to as, QUAD GPU SLI.
Drivers, heat and power are not the only issue. The length of the card, plus the VRAM, also, come into play. A dual GPU card is not standard, which is why we haven't had one in a few generations. The last 90 ending card was the GeForce GTX 690, which pinned against a GTX 780 has virtually the same results according to GPU boss. Compared to a GTX 980, which is half the price of the 690, the 690 outright loses the battle. So, while having a Quad GPU SLI configuration might seem like a nice way to earn respect, spending $1245 for a card that loses to a 649$ card will only make you look like you don't know where to spend your cash. Oh, and did I mention that the 690 and 970 have nearly the same score on GPU boss, for a third of the price.
Host : Steve Smith | Music : Jonny Lee Hart | Editor : Steve Smith | Producer : Zed Axis Productions