PLX PEX 8608 Chip

[Met-AL]

How big of a deal is the PLX PEX 8608 chip on the Z68 motherboards?

I can't find specific info on what is disabled when you run a 2nd or 3rd graphics cards in motherboards that don't have the chip.

I see the Asrock Z68 Extreme4 (Intel Z68) Motherboard and the ASUS P8Z68 Deluxe have the chip, other motherboards don't have them.

xbit says:
http://www.xbitlabs.com/articles/mainboards/display/asus-p8z68-deluxe.html

The 16 PCIe 2.0 lanes available in the CPU can be split up into two 8-lane groups by the chipset, so it is natural for Z68-based mainboards to have two graphics card slots. But when a third graphics slot is added, the CPU can't give any more PCIe lanes whereas the chipset's PCIe interface is needed for the rest of interfaces and controllers. Therefore the third graphics slot is usually allotted but one PCIe lane or four lanes at the expense of some other interfaces. The list of features that are disabled when the third graphics slot is used can usually be found in small print somewhere in the mainboard specs. These are usually onboard SATA or eSATA controllers, USB 3.0, IEEE1394 (FireWire), PCI or PCIe x1 slots. The P8Z68 Deluxe is different as it employs a PLX PEX 8608 controller to have an additional eight PCI Express 2.0 lanes so that you could use all the graphics slots without losing anything in other features.

 

[iconiK]

It's a PCIe switch, just like NF200, except PLX chips are faster and use a whole lot LESS power than NF200. The downside is they cost more.

 

[Met-AL]

are they important? In my case I am going to run only two GPU's at the moment.

 

[Rizen]

are they important? In my case I am going to run only two GPU's at the moment.

Wouldn't that depend solely on if you need that features that are shut off if you use more than 2 GPUs?

 

[iconiK]

Wouldn't that depend solely on if you need that features that are shut off if you use more than 2 GPUs?

Namely USB 3.0 and extra SATA 6Gb/s. Why they are shut off beats me - the damn chipset gives you eight PCIe 2.0 lanes, how the crap are they not enough? Send four to the slot, send four to LAN, USB and SATA.

 

[Met-AL]

Namely USB 3.0 and extra SATA 6Gb/s. Why they are shut off beats me - the damn chipset gives you eight PCIe 2.0 lanes, how the crap are they not enough? Send four to the slot, send four to LAN, USB and SATA.

I think it's the CPU that has the 8 PCIe 2.0 lanes, and I think they are used in pairs.. so each GPU slot takes two lanes.

 

[iconiK]

I think it's the CPU that has the 8 PCIe 2.0 lanes, and I think they are used in pairs.. so each GPU slot takes two lanes.

The CPU has 16 lanes, and they go two the two main x8 slots (or a single x16). The Xeons do have an extra 4 lanes off the CPU that can be accessed via a C202 or C204 chipset AFAIK.

I'm talking here purely about the ones available from the chipset.