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I recently built my brother a new computer, and after I completed installation of everything, and had installed the ATI Catalyst drivers, I noticed that the card was running in x8 mode in a PCIe x16 slot. I checked to make sure that I had installed the card into the correct slot for single discrete-graphics operation, and I had.

It turns out that I had been careless in reading the motherboard manual, and that it had come with a little slot filler that had to be installed when only 1 discrete graphics card is in the system.

My question is, what is the purpose of this? I have seen other systems that did not require such an accessory/whatever it is, and worked at the full speed of the slot with the card. Why did this motherboard need to include this design feature?

Motherboard on Newegg: link

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It's a 'technology' used by older SLI/crossfire motherboards.
There is either a small "slot card" between the two PCI Ex 16x slots, or this dummy card.

When you install a second card, on these mainboards the speed usually gets 1/2, so 8x and 8x on both cards. That's why.

On my new MSi mainboard this is completely missing and it says 4xPCIeX16 .. beats me if that's true. :)
(On my old MSI, I had a card. Can't recall it's name right now..)

Found the switch:
http://www.nvnews.net/reviews/msi_p6n_sli_platinum/page_4.shtml

It is a small, ejectable card.

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Ok, that's somewhat enlightening, but I was wondering what the dummy actually did to the routing of information through the discrete card. It seems to me that if there was nothing in the 2nd slot, it wouldn't make any difference whatsoever to the first slot. I didn't really find anything in that HardOCP article that said what that did, just that it did it. – blackmastiff Dec 15 '10 at 18:17

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