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VGAs @ PCI-E x1 Support, why most MBs does not support it?

Discussion in 'Motherboards & Memory' started by Shivansps, Mar 3, 2009.

  1. Shivansps New Member

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    Is not the first time ive read ppl cutting off the end of pci-e x1 slots in mini-itx mbs to place a VGA on them, for some reason this works with the most mini-itx mbs on the market.

    After reading this http://www.tomshardware.com/reviews/sli-coming,927-4.html article i decided to try myselft, taping the lanes on my 4670 to see if it works at lower pci-e speed link.

    I never tryied x2, but the last working speed is x4, at x1 the card will not longer boot.

    This is strange, since all cards are made to work on any pci-e link speed, the MB itselt should detect the speed based on the number of lanes being used.

    Not happy enoght with this result ive decided to try out cutting off the back end of one of my pci-e x1 ports since my mb (Asus M3N78-PRO) is not longer in warranty.
    The result was the same, my card cant boot on x1 pci-e port. The tomshardware article points out that the problem are the MB bios, and not the VGA cards.

    There is ANY tecnical reason for vga cards not working at x1 link? or any diference in a "official" PCI-E x1 card of a PCI-E x16 card with taped lanes?

    Ive some friend who tryied this and got the same results, only one of my friends who has a mini-itx mb in its HTPC, a Intel DG45FC made it work in it, he cutted off the back end of the pci-e x1 slot and placed a 9600GSO of his main pc on it, and work perfectly.

    I wonder if this can be made to work modding the bios. Since DFI gaved a bios fix to tomhardware in two hours, something say me that this is trivial.
     
  2. Silverel

    Silverel New Member

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    I've only ever heard of it working with an x4 slot. Does it have an external power connector? If not, the power supplied by an x1 slot might not be enough.
     
  3. hat

    hat Enthusiast

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    As Silverel said, the 4670 does not have an external power connector, so the power supplied by a pci-e x1 slot will not be enough. I would never run any card without an external power connector in anything less than a x16 slot, also I would never run a pci-e 2.0 card in a pci-e 1.1 or 1.0 slot if said card does not have an external power connector.
     
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  4. Mussels

    Mussels Moderprator Staff Member

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    its just power as they have said. if you tried with a card that used an external power connector there is still no guarantee it would work, as the cards use ground wires on some of those PCI-E connections.
     
  5. u2konline

    u2konline

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    lol i just found out like a couple days ago that you can actually use a pciex16 / 2.0 card in a pcie 1.1 or 1.0 slot. You should try it, just to see how well your performance is. :laugh:
     
  6. hat

    hat Enthusiast

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    Try it? I live it. My 9800gt is PCI-E 2.0 but my board only has 1.1 slots. I get along just fine. It's not the performance (speed) of PCI-E 2.0 over PCI-E 1.1 that concerns me, it's the power requirements. PCI-E 1.1 slots provite 75w of power and PCI-E 2.0 slots provide 150w of power. So, a PCI-E 1.1 card with a single 6-pin external power connector (for example an 8600gts) can draw a maximum of 150w. This is the same power draw as a PCI-E 2.0 card without any external power connectors, for example the AMD HD4670; this card is PCI-E 2.0 and it has no external power connector so it can draw a maximum of 150w because of the PCI-E 2.0 spec, just like the PCI-E 1.1 8600GTS with a single 6-pin external power connector, but the 8600GTS is different because it can only get 75w from the slot and 75w from the power connector which totals 150w. That is why I would never run a PCI-E 2.0 card such as the AMD HD4670 in a motherboard like mine that only has PCI-E 1.1 slots; my board only provides 75W of power through the slot, but since the HD4670 is PCI-E 2.0, it expects to be able to draw up to 150w but I can only provide 75w which translates to possible power starvation.
     
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  7. u2konline

    u2konline

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    Interesting information. :) But you get along just fine, and you haven't had any major trouble, so i wouldn't worry about it. Thats nice that pcie 1.1 can do that. How old is your rig anyway?
     
  8. hat

    hat Enthusiast

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    I don't worry about it because the 9800gt has an external power connector. I've run into no stability problems and it even overclocks quite well so it's getting plenty of power. I plan on keeping this computer the way it is without upgrading for quite a long time. Just about the only thing I think I will ever do is get an x-fi card that has the x-ram, but that will probably be for my birthday which is down the road in June...
     
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  9. Shivansps New Member

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    Good point since my only friend who made this to work has a 9600GSO, so it has a external power conector... But, ive checked the pin out of the PCI-E and it says that the power supply part is on the left side...

    http://pinouts.ru/Slots/pci_express_pinout.shtml

    Maybe the cards uses the GNDs of the data lines?

    Anyway, in the article posted above, (and there is a newer one that i cant find now), say this:

    more info here...
    http://thebsdbox.co.uk/?p=21

    Also, ive tried my HD4670 on my older K8NGM, the card does NOT boot at any speed below x16, so i think is most likely a bios issue.

    I wonder if the bios can the modded?
     
    Last edited: Mar 3, 2009
  10. Shivansps New Member

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    OK, a friend toll me that its HD3850 was working @ x1 on its EP35-DS3L.

    So i asked him to exchange our cards for a day to test this, well, my HD4670 is working at @ x1 on the gigabyte, and his HD3850 does not boot on mine...

    SO is a confirmed bios issue, i wonder if there is any way to mod it.
     
    Last edited: Mar 6, 2009
  11. BrooksyX

    BrooksyX

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    I have an onld ati x300. I wonder if it would work at 1x. The power draw shouldn't be that much on it.
     
  12. Shivansps New Member

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    There is not such of thing like powerdraw problem when the card is running at x1, since the power lines are to the left, and so, they are unaffected and are the same for all speeds.

    MB BIOS not supporting cards running at lower speed is the problem, that why im been asking if someone can take a look at it, since i whould like to place another card in the pci-e x1 slot.
     
  13. newtekie1

    newtekie1 Semi-Retired Folder

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    Exactly what Shivansps said. There is no power issue, all the power is supplied by the little part before the notch, that all cards have regardless of if they are an x16 or an x1 card. All the cards get the same amount of power.

    Now as for running PCI-E 2.0 cards in 1.1/1.0 slots. There isn't an issue there either, regardless of if they have a dedicated power connector or now. My HD4670 runs perfectly fine in a PCI-E 1.0 slot of my A8N32. To maintain backwards compatibility, the cards only draw 75w or less, if they draw more than 75w then an external power connector is put on the card. My HD4670 is perfectly stable in the PCI-E 1.0 slot at stock speeds, but it overclocks like complete crap. Though the HD4670's aren't exactly known to be good overclockers anyway. I haven't tried overclocking it in a PCI-E 2.0 slot, but I guess the extra power might help it overclock better.
     
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