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PCIe x16 vs. x8, x4, x1

Discussion in 'Graphics Cards' started by Sasqui, Mar 29, 2007.

  1. Sasqui

    Sasqui

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  2. LiNKiN

    LiNKiN Staff

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    Very interesting read indeed Sasqui! Interesting to see just how much bandwidth the 8800 needs!
     
  3. Pinchy New Member

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    Now we ask ourself - why are there motherboards that have their 2nd PCIe slot at only 4x :p
     
  4. Sasqui

    Sasqui

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    On the second page, they show the duplexing bandwidth - I suspect the 8800 doesn't take advantage of it like the 1900...
     
  5. Pinchy New Member

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    This is pretty much on topic, and i dont want to create a new thread about it.

    With the ASUS p5b deluxe, it says the second PCIe slot (for XF) is 4x. But (refer to expansion slots: http://event.asus.com/2006/mb/P5B/models.html), the P5B deluxe and Wifi editions have


    Sounds weird seeing as its 2x16x PCIe, yet the black is 4x or 2x(...anyways). If you look at the P5B-E plus and the P5B-VM, they have 1x PCIe 16x and 1x PCIe 4x....what the?
     
  6. Sasqui

    Sasqui

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    That's par for all 965 based boards (I think!). My DQ6 is 16x and 4x - both are 16x physical slots, but one only has 4x lanes.
     
  7. Pinchy New Member

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    Damn that sucks :(
     
  8. Completely Bonkers New Member

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    Interesting benchmarking... I'm surprised that Tom's was so late in doing the taping exercise. Many other sites have done it already.

    The summary is that in most real-life situations (not benchmarking tools which are actually only benchmarking the bandwidth), that the performance ratios are: x16=100%, x8=98%, x4=85%. That means, an x8 lane is not noticeable slower than an x16, but an x4 is measurably slower... albeit, only 15% loss. However, Tom's analysis shows these ratios are for ATI GPUs and not nVidia which suffers much more.

    And the interesting fact is that AGP DOES OPERATE as x8 speed. So AGP is not dead (yet).

    It's a shame that the review didn't take X1950Pro or X1950XT card as well, and compare this to X1950Pro/XT AGP. Now THAT would have been truely interesting!

    Personally, I will not be upgrading my mobo until PCIe v2.0, about 6 months away. In the meantime, I will upgrade my GPU... which therefore means I'm looking at an AGP X1950XT. http://geizhals.at/deutschland/a239982.html
     
  9. Pinchy New Member

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    The only problem with having an AGP system is that you can get a good processor or good RAM, or XF/SLi (Thats why I went to PCIe)
     
  10. WarEagleAU

    WarEagleAU Bird of Prey

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    awesome stuff, Ill check it out now.
     
  11. Completely Bonkers New Member

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    Oh, but you can! You can get a Quad Core 2 Duo on AGP! See ASROCK site for many many mobo's. What's also nice, is that if you have 2 or 4 GB of fast DDR... you can use that on a Quad Core 2 Duo too. And it performs pretty well too... because of the better latency of DDR over DDR2 and the big cache of the Core 2 Duo.

    While a whole new PC and memory may be (marginally) faster than the ASROCK setup... you save a BUNDLE not having to upgrade RAM or a good AGP GPU. See my specs as to why I'm not tossing my GPU just yet!
     
  12. Pinchy New Member

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    Wow didnt know that.

    Still though, wouldnt those mobos be expensive? And you are very limited in brands...(not dissing Asrock in any way - ive never used 1 so i dont know what its like)

    But I dont know about overseas, but im sure that the AGP GPU's over here are heaps more expensive than the PCIe ones. Theres a $100 difference between the X1950 PRO's from AGP --> PCIe (Thats over half your PCIe mobo :p)
     
  13. kwchang007

    kwchang007 New Member

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    uh oh, so the whole asus xg station is not going to preform that well.....bummer....
     
  14. DanTheBanjoman SeƱor Moderator

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    Asrock is dirt cheap actually. They're not the best for overclockers or anything, though for normal use they're just fine.
     
  15. Pinchy New Member

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    Last time i checked, which was a while back, the asrock mobo i wanted (PCIe for socket 478) was uber expensive...


    well, i think it was asrock :D


    EDIT - Holy @#$%! They are really cheap :|
     
  16. tkpenalty New Member

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    Yeah.. $70 for a fully fledged motherboard that supports core 2 quad and 1066 mhz as well as ESATA.... PCI-E 16x and 8x.
     
  17. D-rock New Member

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    Yes, thats correct. The P965 chip only supports 20 PCIe lanes. 16 lanes for the blue (on asus mobo) slot and 4 for the black slot. If you have a card in the X1 PCIe slot then the black slot, while its physically an x16 size it will revert to x2 lanes.
     
  18. Pinchy New Member

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    So that means the second card can only run at 2-4x?

    Couldnt you split it, 8x and 8x? Or 10x and 10x :p
     
  19. Behemoko New Member

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    Nice find, I'm glad to see that we haven't yet needed 8x, even 6x would probably be enough for the 8800, so we seem pretty future proofed, (at least for a while anyway, lol)
     
  20. D-rock New Member

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    I guess that depends on your mobo. I have the P5B deluxe and it doesnt allow for that. But i know that some mobo's that use the 965 chip and do crossfire thats how they do it.
     
  21. Pinchy New Member

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    Maybe we will get a BIOS update that'll enable it :)
     
  22. Eric_Cartman

    Eric_Cartman

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    i think the bridge between the cards takes care of the need for the extra bandwidth of the second slot

    which is why crossfire on boards with a second slot that is only x4 only works with cards that have the bridge connections between them
     
  23. Sasqui

    Sasqui

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    That's entirely possible... even the ATI 3200 chipset in CF runs at x8 and x8 (and a third at x2 for physics)... 16 total lanes, as opposed to 20 lanes on the 965.

    Even the 975 seems to have this limitation... "PCI Express x16 3 (1 electrical x16 or x8, 1 electrical x8, 1 electrical x4) " from the intel 975XBX "Badaxe"
     
  24. Zubasa

    Zubasa

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    Nope.:slap:
    The Crossfire Xpress 3200 chipset is the first to have has dual 16x full speed PCI-E slots. (32 lanes and yes thats what 3200 stand for.)

    The Crossfire Xpress 1600 chipset is the one with dual 8x bandwidth. (16 lanes)
    It has the ability to switch between normal X16 mode and CF mode.
     
    Last edited: Mar 30, 2007
  25. Sasqui

    Sasqui

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    Yep :nutkick: Unless the specs are wrong on newegg, or we're talking about something else.

    PCI Express x16 3 x (2+1 Configuration: 2 Graphics + 1 Physics)
    - 2 ATI CrossFire graphics cards (each operates at x8 bandwidth).
    - 1 ATI Physics graphics card operates at x2 bandwidth.

    http://www.newegg.com/Product/Product.aspx?Item=N82E16813136032

    And from DFI:

    Expansion Slots
    3 PCI Express x16 slots for ATI CrossFire and ATI Physics
    2+1 Configuration (2 Graphics + 1 Physics)
    - 2 ATI CrossFire graphics cards (each operates at x8 bandwidth).
    - 1 ATI Physics graphics card operates at x2 bandwidth.
    3 PCI slots

    http://www.dfi.com.tw/Product/xx_pr....jsp?PRODUCT_ID=5155&CATEGORY_TYPE=MB&SITE=NA
     

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