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Is it possible to plug in PCIe x4 NIC into PCIe x16 slot?

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up vote 8 down vote accepted

Yes, it works just fine, obviously it's only work at x4 speed (8Gbps).

I would check whether the x16 slot can handle the power load of the x4 adapter, it depends on the adapter but I've seen some quite high power draw adapters using x4 electricals without an external power connector such as those you see in higher-end video cards. In some cases system-board manufacturers expect that adapters going into x16 slots will usually use external power connectors so they rate them with a slightly lower power draw capability from the board than from the lower-speed slots. This probably won't matter in your case but I wanted you to be aware.

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Did you mean 8 g bps? – Spiff Mar 9 '10 at 17:57
Yeah, yeah I did, it's called a typo and it's not worth a bloody downvote you pedant. – Chopper3 Mar 9 '10 at 20:22


Not an answer to your question, but something I didn't believe until I had seen it with my own eyes, it is sometimes possible to take a hacksaw to a PCIe x16 card and cut the connector down to fit into a PCIe x4 slot.

"Why on earth would you want to do that?" is the obvious question. Well we inherited half a dozen Poweredge 440s that we wanted to use as workstations, but the built in video card is a very basic one and they don't have a x16 slot, only x8 and x4. We found we could take a generic Geforce 7100 GS card and cut down the connector with a jewellers saw to fit in the x4 slot and it worked. Perfectly in fact! Curiously it wouldn't work in the x8 slot.

I have yet to try this with a top end card. When I win the lottery I'll give it a try :-)


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+1 for using a saw on a video card and making it work. – atom255 Jun 23 '09 at 16:38
+1 for giving it a go – Richard Slater Nov 26 '09 at 18:48
We used to stuff AT (16-bit) ISA video cards into our XT (8-bit) ISA busses back in the day. Sometimes you just had the 16-bit portion hanging out, sometimes you had to cut it off to fit. Worked fine (albeit at a slower speed) on all the cards I tried though! – Brian Knoblauch Mar 9 '10 at 18:52
+1 for being my hero for the day. – ErnieTheGeek Feb 24 '11 at 14:43

Yes it is backwards compatible:

  • PCI-E x1 card will go in a x1, x4 or x16 slot.
  • PCI-E x4 card will go in a x4 or x16 slot.
  • PCI-E x16 card will only go in a x16 slot.

In addition PCI-E 2.0 cards will work in PCI-E 1.0 slots with the above limitations. PCI-E 2.1 incorporates some components of PCI-E 3.0 but without changing compatibility or speed.

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Yes, PCIe is backwards compatible.

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