PCI & PCI Express: are they compatible?

Posted on 2004-08-07
Last Modified: 2010-04-25

I'm looking to buy a new motherboard and need to know about the compatibility of PCI and PCI Express.

Will my existing PCI cards from my old PC work in PCI Express slots on a new motherboard?

Advice is much appreciated.

Question by:timclyma
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Expert Comment

ID: 11742838
According to Intel and this one motherboard they are making it will be the same can skip down to the compatibility section.  I assume this is the case with any PCI Express slot but you may want to check with your motherboard manufacturer before buying.


Accepted Solution

lidsky earned 50 total points
ID: 11742881
No, PCI Express and PCI are two different animals. You can not put a PCI card into a PCI Express slot.

The comments on compatability refers to software, i.e. PCI Express cards will look just like a PCI card to the software, so that no modifications to the OS are needed.

Most mother board manufacturers will probably include PCI slots so that you will not have to upgrade everything all at once. Just like what happened when PCI started to replace ISA.
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Expert Comment

ID: 11742912
According to Intel, unless I am reading this wrong that is not the case...

Form Factor Compatibility  PCI Express connectors are similar in width to existing PCI connectors. In addition, they also share the same PCB dimensions, component height, and support existing ATX and server form factors. The PCI Express add-in cards follow the same height and length requirements as PCI, and utilize the same I/O bracket to secure cards to the chassis.

Though I agree with you lidsky that was my impression of what was going to happen becasue I know initially they were talking about PCI Express replacing PCI and not being compatible due to different slots.  And yes the software will not be affected as all changes are on physical level...that was a plus of upgrading to PCI Express is that the OS or applications, etc....wouldn't need any special software or coinfiguration other than what a PCI card has now.
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Expert Comment

ID: 11742957

Please read that paragraph carefully.

"PCI Express connectors are similar in width to existing PCI connectors" - They're about the same size.

" they also share the same PCB dimensions, component height,"  -  They don't take up any more room than PCI cards.

In other words slot spacing and card sizes won't change, so old cases can still be used. Motherboard size will remain the same.

No where does it say that the slots are electrically compatible.
LVL 10

Expert Comment

ID: 11742966
I guess you are is tricky wording....and that makes more sense too

Assisted Solution

lidsky earned 50 total points
ID: 11743060

Just found this -

If you scroll down you will find a picture of a PCI Express motherboard showing the slots.

You will notice that the PCI Express x1 slots are much shorter than the PCI slots. The PCI Express x16 slot looks about the same as an AGP slot.

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