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4670 in x4 slot - any potential for power issues?

Last response: in Graphics & Displays
April 26, 2009 8:21:32 AM

Hi all

I have a Gigabyte Ga-EG41M-S2H board, which has a PCIe x16 slot that operates at x4. I can say it runs off the ICH7 southbridge and the PCIe specification is 1.0a. Here is a picture of the PCIe x16 (x4) slot in my motherboard:

I found this site which details maximum power in Watts available to certain speed PCIe 1.0a slots and the relevant interest here is x4/x8 = 25W

For video card, I have a HD 4670 which is not overclocked, 512MB PCIe 2.0 card. This card has *no* external power requirements; it is entirely bus-powered.

Question: would there be any problem with supplying enough power to the graphics card? Everything I have read on the net refers to, "No problems, the card will just slow down and use the maximum available number of PCIe lanes," but in those cases, most refer to a card with external PCIe power connector. Is it different in this case since my card obtains all its power via the PCIe x16 (x4 mode) slot?

Right now I have Windows XP installed and via GPU-Z and CPU-Z they have PCIe x16, @ x4 so it all appears working, but I am not sure if I am risking anything. Can anyone reassure me that this will be okay? I'm not worried about speed or decreased performance, just that the card will work and continue to run without issue.

Thank you all!
April 26, 2009 3:57:50 PM

Since the slot is 16x length, it SHOULD supply the needed 75W. If you check out it's product page

It states it has a GPU support list, so I don't know. Check your manual, or download the manual PDF from the site, to try and learn more about it.
April 26, 2009 4:13:47 PM

Regarding the length, it appears purely physical. The actual connections on the back on the PCB don't appear to have any contacts (ie. it looks exactly like a 4x slot on the back of the motherboard).

For the list, that's the first place I checked. I forgot to mention that.. the list doesn't have it, so i can assume it's an out-of-date list or that it doesn't support it. I'm leaning towards the former because:

a) it doesn't list any of the newer low-end, lower power HD4000 series [though i realise these lists arent usually maintained and are usually produced just at the time of product release]

b) the fact that it lists the HD3650 card as compatible. This previous generation card has a TDP of around ~55W I believe. This would use substantially more power than a x4/x8 slot could provide, so the fact that it is listed as compatible must mean that operating in a x4 electrical slot is completely fine for cards only powered by the PCIe Bus.

At least, that's what I hope can be extrapolated.. :D 
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April 26, 2009 5:08:32 PM

A slot of 4x length only provides 25W. Since MB makers produce a 4x slot with 16x length, they intend for you to put in a 16x GPU. While they may supply more power to it, since it's only a 4x slot they may not supply the full 75W. IF the support list only lists low powered GPUs, then the slot may only provide 60W. If it says it can support a 3850, a card that expects to draw 75W from the PCI-E slot plus a few from the external connector, then you should be fine.
April 27, 2009 9:23:43 PM

here is some good info:

the pinout shows that a PCI Express slot's power comes from within the first set (11 pins) on the connector. with that information, I'm happy that you can see it is purely the lanes missing and not electrical power.

that means it would be up to gigabyte's design as to whether they adhere to these power specs. since they've already modified this (PCIe x16 slot) with only x4 lanes, i'm guessing they've designed/allowed power for the full PCIe 1.0a spec of 75W. Only a guess, but it would make the most sense.