PCIe x(1,4,8,16) compatiblity

[Gavin_Capacitor]

Hi, I know that smaller PCIe cards (ex. a PCIe x1 card) will work in a higher slot (ex. a PCIe x8 slot). However, I have heard that sometimes you can put bigger cards into smaller slots, and the PCIe protocol will just negotiate a lower number of lanes. This seems to be at least partially true as the PCIe x4 slot on my motherboard does not have a back (so a PCIe x16 card would physically fit into it.). I wanted some clarification on this. The reason I want to know is that I have a rocketraid 2320 (PCIe x4) and wanted to know if I could put it in a PCIe x1 slot (I am willing to get a dremel and have at it.) - so if anyone knows about this in particular that would be awesome. Thx!

 

[Spleenharvester]

PCIe slots come in a variety of sizes referred to by the maximum lane count they support. A larger card will not fit in a smaller slot but a smaller card can be used in a larger slot. The number of lanes actually connected may be smaller than the number supported by the slot size. While a 16 lane card cannot be used in an 8 lane slot it can be used in a 16 lane slot with only 8 lanes connected. The number of lanes are "negotiated" during power-up or explicitly during operation. By making the lane count flexible a single standard can provide for the needs of high bandwidth cards (e.g. graphics cards, 10 gigabit ethernet cards and multiport gigabit ethernet cards) while also being economical for less demanding cards.

This is from wikipedia. The bits in bold should answer your question.
regards
Spleenharvester

 

[vnf4ultra]

It seems that sometimes cards can work in smaller slots than designed for if the slot has been modified and the board supports it.
Tom's Hardware did tests where they taped off parts of the x16 connector to test the different speeds, here's a comment from their review.

Not every motherboard can be operated at low PCI Express link counts for PCIe graphics. In our initial article, we had to patch the BIOS of a DFI LANParty 925X-T2 motherboard to support the low-bandwidth connections. We also had to try several new motherboards before we found one that would allow us to run the benchmarks.

Second, I found a guy that modified an x8 slot (hot x-acto knife ) to accept a x18 card, so that gives me some hope that such a mod may work.

 

[Gavin_Capacitor]

Thanks for your advice! I actually found an adapter at: http://www.orbitmicro.com/global/pciexpressx1tox4adapter-p-753.html. It goes from PCIe x1 to PCIe x4 (I'm sure it operates with one PCIe lane, but the rest of the card receives power so it can negotiate the one lane and will work.). I do have two questions though:
1. Would it be smarter to just buy the PCIe x1 to PCIe x16 adapter (http://www.orbitmicro.com/global/pciexpressx1tox16adapter-p-1648.html) since I could also plug a PCIe x4 card into that (it would give me more flexibility)?
2. This looks like it will rise the card higher off the motherboard, so is there some sort of special bracket I can get for my card anywhere?

 

[vnf4ultra]

I'm no expert on the technical details of pci express, but I *think* that all the power that the pci-e slot gets would be available in the first (x1) part of the connector. Looking at the diagram of pci-e from toms, I can only see 12v and VCC pins in the first part of the connector. The rest of the pins appear to be signal and ground pins if I'm reading that right.


I think either adapter would work fine, if you don't want to mod your board.

It will be higher, and I've never seen adapters to work with risers like that, but they could exist. You could potentially dremel/bend the bracket of the card yourself to get the screw mounting point to line up.

Anyway...for your benefit, (and mine ) I fired up my pci-e 7800gt card in my pci-e x2 slot. The slot is physically a "x4 slot," but electrically a x2 slot. Everything seemed to work just fine running in the x2 slot. Here's a picture of it.





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[Gavin_Capacitor]

I'm no expert on the technical details of pci express, but I *think* that all the power that the pci-e slot gets would be available in the first (x1) part of the connector. Looking at the diagram of pci-e from toms, I can only see 12v and VCC pins in the first part of the connector. The rest of the pins appear to be signal and ground pins if I'm reading that right.


I think either adapter would work fine, if you don't want to mod your board.

It will be higher, and I've never seen adapters to work with risers like that, but they could exist. You could potentially dremel/bend the bracket of the card yourself to get the screw mounting point to line up.

Anyway...for your benefit, (and mine ) I fired up my pci-e 7800gt card in my pci-e x2 slot. The slot is physically a "x4 slot," but electrically a x2 slot. Everything seemed to work just fine running in the x2 slot. Here's a picture of it.





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Dude! Thats awesome, thank you! You wouldn't happen to have a rocketraid 2320 laying around would you lol

Edit: update: I found this: http://pinouts.ru/Slots/pci_express_pinout.shtml and it seems that all of the power and stuff is in that first 'section' on the card. Everything after that is just more lanes. Looking at this it would seem its possible to plug any PCIe card into any PCIe slot, provided the back as removed so it physically fit.

Also, I cannot seem to find a bracket to work the the PCIe x1 -> PCIe x4 adapter in my previous post. Was wondering if anyone knows of where I could find one, or If there are longer than normal screws to mount cards w/blots for them?