Intel Z77 extra PCIe x4 slot

Discussion in 'Processors and motherboards Intel' started by deltatux, Apr 14, 2012.

  1. deltatux

    deltatux Ancient Guru

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    Hey guys,

    I'm trying to understand these new Z77 motherboards coming out with the extra PCIe x16 slots running at x4 mode. According to the ASUS P8Z77-V motherboard manual which is in French (there's no English manual to download which is weird).

    It states:
    Which translates to:
    So does that mean that if I slot a PCIe x4 card in the PCIe x16_3 slot, then the other PCIe x1 would not work? Conversely, If I slip a PCIe x1 in the first slot, would the PCIe x16_3 work at x4 or would it downgrade to X1 regardless?

    If so, then why the hell did they bother putting another PCIe x16 slot there, I find it kind of useless if I insert a card there and it disables the other PCIe slots.

    deltatux
     
  2. ---TK---

    ---TK--- Ancient Guru

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    Look for a review on that MB maybe. My 3 pcie slots are 2x8x with sli and 1 4x slot I think
     
  3. fr33k

    fr33k Ancient Guru

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    if its like my old one it forces the 16x to run at 8x.
     
  4. deltatux

    deltatux Ancient Guru

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    No no man, the PCIe x16 slot at the very bottom of these boards function at only x4.

    Here's an example from the ASUS P8Z77-V motherboard which I'm thinking of getting:
    [​IMG]

    See how the bottom PCIe x16 slot is there? So I'm confused on how it works. Does it mean that when PCIe x1_1 and PCIe x1_2 are plugged in PCIe x16_3 runs at x1 speed and if I slip in a PCIe x4 card there, it disables both the PCIe x1 slots?

    Apparently they're shared from what I'm reading.... can anyone confirm?

    deltatux
     

  5. fr33k

    fr33k Ancient Guru

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    I meant the same- Link mode forced mine at 8x instead of 16x no matter what as long as it was in link mode. Judging by the translation link mode with any added cards simply makes it 1x.
     
  6. deltatux

    deltatux Ancient Guru

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    So I don't get why these board manufacturers put a x16 slot there if it's going to run x1 anyways >.>"

    Thanks man

    deltatux
     
  7. Pill Monster

    Pill Monster Banned

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    That French manual is wrong or else it's been translated incorrectly.
    The PCIe x1_2 shares it's bandwidth with SATA6G_E12 and the black slot runs at x4 mode.

    http://www.asus.com/Motherboards/Intel_Socket_1155/P8Z77V/#specifications
     
    Last edited: Apr 15, 2012
  8. deltatux

    deltatux Ancient Guru

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    That's what it's written and that's what I translated from French to English (no I didn't use a translation service).

    EDIT: I'm guessing since the two PCIe x1 slots shares bandwidth from that PCIe 2.0 x16 slot at the bottom of the board, it by extension shares data with that SATA 3 port.

    I do believe that by default that bottom slot runs at x1 speed, even ASUS's Sabertooth Z77 manual states that:
    deltatux
     
    Last edited: Apr 15, 2012
  9. Sash

    Sash Ancient Guru

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    Why don't you just read the specs from the mobo's website form Asus?

    2 x PCIe 3.0/2.0 x16 (x16 or dual x8)
    1 x PCIe 2.0 x16 (x4 mode, black)
    2 x PCIe 2.0 x1
    2 x PCI

    And anyway, sandy and ivy bridge have 16 pcie lanes on the CPU, the rest of the lanes are on the Z77 chipset. Look at these block diagrams for the Z77 chipset:

    [​IMG]

    And BTW, intel lied about series 7 boards supporting pcie gen 3, it was never meant for the chipset, only Ivy Bridge has those 16 pcie gen 3 lanes!
     
  10. Pill Monster

    Pill Monster Banned

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    It runs at x4.

    Edit-
    This might help...

    [​IMG]
    http://www.hardwaresecrets.com/article/ASUS-P8Z77-V-DELUXE-Motherboard/1528/2
     
    Last edited: Apr 15, 2012

  11. Saad

    Saad Master Guru

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    yes pretty much..i have a p8p67 and when i put anything in the 4x slot, i can either run it at 4x or at 1x...at 4x the second usb 3 controller and the pcie 1x slot stop working
     
  12. BLEH!

    BLEH! Ancient Guru

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    You've automatically got a mix of gen2 and gen3, 8 of one from the SB and 16 of the other from the "NB"/CPU. My guess would be that the 2 x1's and the x4 are from the SB. ASUS aren't very helpful about disclosing what's connected to what in PCIe, I've been trying to get some info out of em for ages but they reall'y aren't very helpful on the matter.
     
  13. deltatux

    deltatux Ancient Guru

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  14. BLEH!

    BLEH! Ancient Guru

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    Going off that deltatux, it looks like the 16 Gen3 lanes off the CPU are splittable into x8/x8 and that bottom x4 slot is coming off the SB. IIRC X77 allows the 16 lanes to be split x8/x4/x4, but theres an additional x4 from the SB as well. You've probably got a few extra controllers stuck on the SB, hence the 8 going down to 4.
     
  15. sykozis

    sykozis Ancient Guru

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    That's been known to happen....
     

  16. BLEH!

    BLEH! Ancient Guru

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    At least Gigabyte have the decency to whack a block diagram in their manuals. ASUS have been less than helpful in providing one for my motherboard.
     
  17. sykozis

    sykozis Ancient Guru

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    If I had a nickel for every time Asus has been "less than helpful"....I'd be retired already....lol

    My HD7870 is the first time they've even been remotely helpful....

    After-sale support is the main reason I stick with ASRock....
     
  18. BLEH!

    BLEH! Ancient Guru

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    This is why I was wary about getting an ASUS board, but I can't fault it thus far. If I do have any problems, though I'll just take it back to Scan, who've been more than helpful in recent years with faulty stuff. I'm just wary about going back to Gigabyte after 2 X58-UD3Rs died on me, but that coulda been a PSU issue. ASUS do make good stuff, just don't fix it well when they need to.
     
  19. Sever

    Sever Ancient Guru

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    actually, you still need a motherboard that supports pcie3.0. if you run ivy bridge on a p67/z68 board that doesnt support pcie3.0, then it will run at pcie2.0. motherboard must have all the hardware required to support pcie3.0 for ivy bridge to use its pcie3.0 lanes.
     
  20. automaticman

    automaticman Master Guru

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    There are 16 3.0 lanes available from the CPU. The first 8 of those lanes connect directly to the PCIe1 socket, the other 8 lanes go to a PLX bridge chip.

    When only one PCIe slot is populated, those 8 lanes are routed back to the PCIe1 socket to give it a full 16 lanes.

    When the second slot is also populated, the 8 lanes from the PLX chip are routed instead to the PCIe2 socket.

    This is also how Z68 works. The Z77 chipset also adds the ability to route 4 lanes from the PLX chip to an optional Thunderbolt controller, making PCIe2 x4. This is what is noted in the block diagram.

    The Z77 chipset itself also has pcie lanes, but they are all 2.0 lanes. These lanes are used to add additional SATA controllers (like Marvell) or a second gigabit NIC, but 4 lanes can also be routed to PCIe3.

    Some manufacturers will disable some addons if you plug something into that PCIe3, because there are only 8 lanes to go around. The higher end ASUS boards us another PLX chip to intelligently switch lanes to where they are needed, when bandwidth is needed, so that plugging in pcie3 doesn't deactivate a pair of SATA ports or something.
     

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