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
  ASUS
P8Z77-V Premium
Gigabyte
G1.Sniper 3
ASRock
Z77 Extreme9
ECS
Z77H2-AX
EVGA
Z77 FTW
Price $450 $280 $350 $310 $310
Size ATX EATX ATX ATX EATX
NIC Intel 82579V
Intel 82583
Killer E2200
Intel
Broadcom
BCM57781 x 2
Realtek 8111E Marvell
88E8057 x 2
Teaming - No Yes No -
Audio Realtek ALC898 CA0132 Realtek ALC898 Realtek ALC892 Realtek ALC889
VGA No Yes No Yes No
DVI-D No Yes No No No
HDMI Yes Yes Yes Yes No
DisplayPort Yes Yes No No Mini
Thunderbolt Yes No No No No
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 -
Fan Headers 6 5 7 3 5
Warranty (NA) 3 Years 3 Years 3 Years 3 Years 3 Years

 

Conclusion: EVGA Z77 FTW
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  • mayankleoboy1 - Wednesday, August 22, 2012 - link

    Where are the GPGPU benchmarks? AFAIK, those are affected by the PCIE 3.0 bandwidth, as shown in the HD7970 review.

    Games are more or less happy with a PCIE2.0 x8 .
    Reply
  • MrSpadge - Thursday, August 23, 2012 - link

    A few GP-GPU apps are affected, most aren't. Even PCIe 3 is slow as hell from the perspective of the GPU, so you try to avoid external communication as much as possible. Reply
  • TimoKyyro - Wednesday, August 29, 2012 - link

    I was hoping to see some GPU rendering too. I'm using CUDA on Blender and I really need more GPU power. It would be nice to know if there is a difference between 4x 680 or 2x 690 on different PCIe setups. Reply
  • extide - Wednesday, August 22, 2012 - link

    Thanks for providing the diagrams of lane routing. I wish ALL manufacturers would supply a diagram with their boards so you know how to set it up when you are building a system. Sadly, these diagrams are the exception, not the rule. :( Reply
  • processinfo - Wednesday, August 22, 2012 - link

    For me only EVGA seems worth consideration (I don’t like a fan on chipset though).

    I have few requirements that others do not meet.

    I want PS/2 keyboard port (don’t care about mouse). I don’t see it as legacy. It is still superior to USB for keyboard. Works on interrupts instead of pulling, allows as many keys pressed without ghosting as you wish (know it probably does not matter in real life but I like that anyway).

    Display port output is mandatory for me these days. While it is true that this kind of mobo will run dedicated graphics card (or more than one for that matter) I like to have output here for possibility to use it with CPU graphics if my graphic cards breaks and needs replacement (I had that happen and waited almost two weeks for new one). HDMI is no go because does not support high enough resolution.

    Gigabyte is out for me because audio chip. Maybe it is better but it does not do 7.1 and I will lose two channels in my Tiamat 7.1 headset.
    Reply
  • rwpritchett - Wednesday, August 22, 2012 - link

    You should check out some of the newer USB keyboards. I don't know how they do it, but some of them can now do full NKRO without PS/2. My Nighthawk X9 can do full NKRO over USB. Reply
  • processinfo - Thursday, August 23, 2012 - link

    Interesting but this is not possible with standard USB keyboard protocol. If it does that it has to use some tricks and most likely custom keyboard driver.

    Also I have Thermaltake Meka G1 that I like and I purchased because I got tired replacing membrane keyboards so I rather buy motherboard with PS/2 then new keyboard.

    My point is that at this price point and clearly meant for gamers (who else is using more than one graphic card in non-workstation pc) they should think about such details especially when they go overboard with other ports, e.g., who needs all 4 kinds of display output on gaming mobo, or 10 USB ports on back plate alone (if you need plenty you can have them on bracket connected to header).
    Reply
  • MacGyverSG1 - Wednesday, August 22, 2012 - link

    I loved the review. The G1.Sniper 3 was on my short list for a while. Could get back on, though.

    I'm waiting for the ASUS Maximus V Extreme to get tested next.

    I only need a motherboard to complete my new build. I plan on running this new rig for 6+ years so I want a board that can keep up with the times.
    Reply
  • just4U - Thursday, August 23, 2012 - link

    I am staying away from the Rampage/Maximus lines from Asus this time out as Gigabyte has pretty much brought better value accross the board on their gamer boards. I don't expect Asus to catch up till the next chipset.. Reply
  • goinginstyle - Thursday, August 23, 2012 - link

    I tried the G1 Sniper 3 and returned it a few days later. The audio was a significant downgrade from the Assassin series, EFI is clunky at best and the board had serious problems with a GSKill 16GB 2666 kit, not to mention the lousy fan controls.

    Purchased a Maximus Formula V and never looked back as the EFI, Fan Controls, Clocking and Audio are much better in every way compared to the Sniper board. There is no way Gigabyte has brought better value than ASUS with the Z77 chipset. You get what you pay for and the GB is overpriced once you actually use the board and compare it to ASUS or even ASRock.
    Reply

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