Four Z87 Express Motherboards For Three- And Four-Way SLI

Making Z87 Express Three-Way SLI-Capable

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We've seen incremental updates to Intel's processor architectures yield small performance benefits in games for the past several generations. However, a great many enthusiasts dislike some of the platform restrictions Intel put in place. For instance, CPUs built around the LGA 1156, 1155, and 1150 interfaces have integrated PCI Express controllers limited to 16 lanes of connectivity. Of course, that's a great way to help minimize latency. But Nvidia's official stance is that those available lanes support a maximum of two GeForce graphics cards. A third would force you to split into x8, x4, and x4 links. So what's a fan of three-way SLI supposed to do?

Stepping up to LGA 2011 gives you access to 40 lanes of third-gen PCIe, but you also have to take an architectural step backwards. Up until Intel launched its Ivy Bridge-E-based chips, you actually had to take two steps back. And beyond higher-priced components, you're talking about using more power and generating more heat, too.

But there's a solution, which isn't particularly new. Used to enable AMD's and Nvidia's fastest dual-GPU graphics cards, PLX Technology's ExpressLane PEX8747 48-lane PCIe 3.0 switch acts a lot like a repeater hub, broadcasting the same data to multiple devices, turning 16 lanes on one end of the switch into 32 lanes on the other, without dividing bandwidth (since CrossFire and SLI require all GPUs to receive identical data).

The usual marketing caveats apply, beginning with PLX calling this a 48-lane switch when, again, it takes 16 lanes on one end and facilitates 32 on the other. Moreover, three- and four-card configurations do cause bandwidth division, cutting dual 16-lane links into eight-lane interfaces. And finally, there’s the slight latency penalty of adding another component, though that seems minor considering both graphics vendors drop the switch onto their GeForce GTX 690 and Radeon HD 7990 without negative consequence.

Three of the above boards have a fifth PCIe x16 slot, but they're all limited to four x16 cards. Located between the first and third x16 slots, the fifth x16 interface is wired directly to the CPU, bypassing the PEX8747 bridge. Anyone not interested in three- or four-way SLI would be better off buying a less expensive motherboard without the PLX switch, so the folks in the market for these platforms can just go ahead pretending the extra slot isn't even there.

Two of the boards in today’s test offer Intel’s Thunderbolt technology, which pairs DisplayPort graphics and PCIe in a single serial signal. Compatible devices eat into both cable bandwidth and the Z87 Express chipset’s eight PCIe 2.0 lanes however, requiring ASRock and Gigabyte to add yet another PLX bridge, the four-lane PEX8605. Adding storage devices to the mini-DisplayPort connectors forces displays down from 4K-capable to a maximum of 2560x1600, while on-board devices and PCIe x1 slots are similarly made to share bandwidth over the PEX8605.