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Does Thunderbolt for Z77 motherboards with Ivy Bridge processors use the PCH or CPU PCIe lanes?

post #1 of 4
Thread Starter 
When used with an Ivy Bridge processor, the Z77 chipset provides 16 PCIe 2.0 (or 3.0 if the video cards are 3.0 compliant) lanes from the CPU, and 8 PCIe 2.0 lanes from the PCH. However, what I am not clear about is whether-or-not Z77 motherboards that provide Thunderbolt support (such as the optional expansion card Asus will provide, or the built-in Thunderbolt port for the MSI Z77A-GD80) use the CPU or PCH PCIe lanes. The AnandTech preview of the MSI Z77A-GD80 appears to indicate that the Thunderbolt controller is connected to the PCH, and the expansion card slot that can be used to add Thunderbolt support to Asus Z77 boards also appears to be connected to the PCH. However, this diagram appears to indicate that Thunderbolt uses the CPU's PCIe lanes:
546
So which one is right?
post #2 of 4
depends on the implementation. I think most motherboard makers are using PCH instead of CPU as no one would want to buy a board if it was only on the CPU lanes lol. Intel is stupid. I know GB is tapping into the FDI which is the display data link from CPU to PCH.
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post #3 of 4
Thread Starter 
Quote:
Originally Posted by Sin0822 View Post

depends on the implementation. I think most motherboard makers are using PCH instead of CPU as no one would want to buy a board if it was only on the CPU lanes lol. Intel is stupid. I know GB is tapping into the FDI which is the display data link from CPU to PCH.

Hmmm...yeah it does seem more likely for motherboard manufacturers to use the PCH's PCIe lanes rather than the CPU's lanes. Giving up those 4 CPU lanes could negatively affect Crossfire and SLI performance. Using the PCH's lanes could be more easily managed. I am personally considering getting the Asus P8Z77-V Deluxe, because it appears to use a PLX chip to manage the PCH's PCIe 2.0 lanes. That should allow the Thunderbolt add-on card and the other controllers tapping into the PCH lanes to operate.

The one thing I do not understand is why would a Z77 motherboard that uses the PCH lanes for Thunderbolt require an Ivy Bridge processor for Thunderbolt to work? I don't see how a Sandy Bridge processor would impede the use of the PCH's 8 PCIe 2.0 lanes.
post #4 of 4
I know now, GB's will be through the PCH.
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