Four Multi-GPU Z77 Boards from $280-$350 - PLX PEX 8747 featuring Gigabyte, ASRock, ECS and EVGAby Ian Cutress on August 22, 2012 9:15 AM EST
Conclusion: PLX 8747 and Multi-GPU Setups
Any modern day computer that uses more than two PCIe devices is considered a niche category. For the most part, we have users with a single GPU, then a mix with add-in audio cards, and dual GPUs. When we hit three GPUs, we are technically in a niche category to which the rich and wealthy are welcome. Despite this, from talks with ASUS, despite the fact that a product may be geared towards a niche market, that product may sell well to the standard market if it is perceived to be good.
Focusing on Z77 and Ivy Bridge, the default setup for Ivy Bridge allows a three way PCIe 3.0 GPU setup, with the lanes adjusted into x8/x4/x4 layout (or various crippled configurations if the chipset lanes PCIe 2.0 are used). This is the only way to arrange the lanes from the CPU. In order to do more with the package, we need a switch – specifically, we turn to the PLX PEX 8747.
In the simplest way of describing the PEX 8747 chip, it allows motherboard manufacturers to direct PCIe 3.0 lanes however they want to the slots. This chip takes either eight or sixteen of the CPU PCIe lanes and with come clever electronic magic (we believe a FIFO multiplexer) manages to give access to 32. These 32 lanes can be distributed as they wish, and offer a large array of different configurations in a Z77 motherboard. It is these configurations that determine efficiency, power usage and performance. It is also up to the motherboard manufacturers to decide which layout they wish to use.
The one downside is the cost of the chip. When I reviewed the ASUS P8Z77-V Premium, I speculated that this chip costs in the region of $40. Since that review, one of our readers got in contact and shared with me the pricing his company gets from their distributor:
Many thanks to Krunal Desai
Thus for a batch of 500 or more of these chips, pricing is in the region of $85 each, which does not include implementation. After some back and forth discussion with Krunal, we came to the conclusion that it was obvious that the motherboard manufacturers were not paying these amounts – they likely had some distribution deal with PLX as these chips are likely to be around for a long while until PCIe 4.0. To add more to this, when publishing the ASUS Premium review, I did speak with ASUS regarding my suggested costs of each of the components on that board and they did not blink when I suggested $40 for the PLX chip. Had they been paying more, it would have been pointed out to me to emphasize the value of the board. Thus I would expect $40 to be a reasonable amount for large manufacturers (based on my testing of the boards in this roundup, ECS may be paying more than most for the chip).
If a manufacturer wanted to be totally nuts, they could implement two on a motherboard. Actually, ASRock have done that, on their X79 Extreme11 – the two PLX chips fund an x16/x16/x16/x16 PCIe slot layout with an LSI SAS RAID chip onboard. We are in the processes of testing and reviewing this board!
To summarize the PLX PEX 8747 usage on the current motherboard scene: the chip itself allows manufacturers to work magic with PCIe layout and lane allocation, especially when the market niche is crying out for better layouts and more bandwidth. For the regular gamut of single GPU users who require little more than a NIC, some USB devices and a SATA drive or two, there is no need to reach higher than $210 to get all you need. But going for a PLX PEX 8747 motherboard brings with it a variety of extra functionality alongside the PLX chip in order for motherboard manufacturers to make the distinctions between PLX and non-PLX.
From this review, out of the four motherboards tested, there really is only one motherboard that can take home any sort of prize. The Gigabyte G1.Sniper 3 is a well built product and a great start to a PLX PEX 8747 focused build.
The following table represents a quick comparison guide to the four boards tested today, as well as the ASUS P8Z77-V Premium reviewed previously.
|Board Comparison Chart|
BCM57781 x 2
88E8057 x 2
|Audio||Realtek ALC898||CA0132||Realtek ALC898||Realtek ALC892||Realtek ALC889|
|WiFi||Yes||Yes (PCIe)||Yes (PCIe)||Yes||No|
|SATA Controllers||Marvell 9320||Marvell 9172||ASMedia ASM1061||ASMedia ASM1061||Marvell 9182|
|SATA 6 Gbps||6 + 2 eSATA||6||6||4 + 2 eSATA||4|
|SATA 3 Gbps||3 + 1 mSATA||3/4 + 1 mSATA||4||2 + 1 mSATA||4 + 2 eSATA|
|USB 3 Controllers||ASMedia||VIA VL810||Etron EJ188||Texas Instruments||ASMedia ASM1042|
|USB 3 + 2||6 + 6||10 + 4||12 + 8||6 + 6||6 + 10|
|mSATA SSD||32GB LiteOn||No||-||No||-|
|Warranty (NA)||3 Years||3 Years||3 Years||3 Years||3 Years|