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PCIe x4 card in a x1 slot

Last response: in Components
December 30, 2011 4:21:08 PM


I have a board with an x1 slot empty. Il have the need to add a dual port NIC which come on a x4 card.
I also need to use a riser for my low profile home system, like these

These risers accept x4 cards and fit in an x1 slot.

Is that supposed to work? I thought that you could insert a x1 card in a x4 slot, but not a x4 card in a x1 slot.
Am I correct in this?

Many thanks for your PCIe insights!

Kind regards, Joost

More about : pcie card slot

December 30, 2011 4:28:08 PM

If you can physically plug it in fine, then it will work. However, it will function at the x1 speed.
December 30, 2011 5:42:34 PM

Well, you are correct. Physically you can insert a 1x card into a 4x slot and it will work fine, but the 4x connector won't fit in a 1x slot (for a reason) and likely will not work even with the adapter. The link you provided comes up to a 404 Not Found HTML error for me but, I've heard about those risers before. Think about it this way. Your trying to plug in a 220 volt appliance into a 110 socket.
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December 30, 2011 6:41:39 PM

PCI-Express is split into lanes to provide bandwidth. If you shove a device into a one lane slot that is designed to be in a 4 lane slot, something is bound to not work right. It's like shoe-horning a size 9 shoe onto a size 12 foot.
December 30, 2011 9:26:57 PM

OK. Thanks for your insight.

I'm fine with the idea of getting only 10Mb/s performance per port. My question is really wether it will work? Does a x4 card have an idea of the slot it's plugged in or is anything beyond x1 just "lanes"?
December 30, 2011 10:13:12 PM

It should work if the specifications are implemented correctly. Lanes are negotiated by both parties.
A PCIe 1.0 x1 link is roughly equivalent to a PCI link. So maybe 150-200MB/s is still achievable (250MB/s on paper), considering that the x1 link is never shared. And if PCIe 2.0 can be used, then the paper limit goes to 500MB/s.
January 1, 2012 2:51:19 PM

That's helpfull. I appreciate it. I'll buy it and let you know wether it works.