pci x8 - is it compatible with x16?

[MarinoFSU]

Can I put a pci x16 video card in the pci x8 slot? If not does anyone know what I can do with the x8 slot?

Thanks,

Chris

 

[klah]

Can I put a pci x16 video card in the pci x8 slot?

No.

If not does anyone know what I can do with the x8 slot?

Not much: http://www.pcisig.com/develope...integrators_list/pcie/

 

[MarinoFSU]

That didn't help much. It doesnt really say specifically.

 

[klah]

Originally posted by: MarinoFSU
That didn't help much. It doesnt really say specifically.

Didn't say what specifically? That list is every product that has been PCIe certified. The only PCIe devices available that do not currently require x16 are a few network devices.



If you are looking for card/slot compatibility there is a table here: Table 3. PCI Express Card Interoperability

 

[Matthias99]

Originally posted by: klah

Originally posted by: MarinoFSU
That didn't help much. It doesnt really say specifically.

Didn't say what specifically? That list is every product that has been PCIe certified. The only PCIe devices available that do not currently require x16 are a few network devices.

If you are looking for card/slot compatibility there is a table here: Table 3. PCI Express Card Interoperability

This is a bit confusing, but SLI motherboards are going to have two x16-sized slots that run at x8 speed. I believe all PCIe parts are required to be able to run at lower speeds like this. I don't know of any consumer motherboard planning on coming out with a physical x8 slot, nor of any graphics cards currently planning a PCIe x8 variant.

 

[VirtualLarry]

I thought that they were supposed to include a "notch" in the connector on the card itself, between 1x/4x/8x/16x, so that any PCIe card would fit into any PCIe slot, and scale down the number of PCIe "lanes" that it could utilize for bandwidth. At least, I heard that was the case with 1x vs. 4x PCIe cards, that a 4x PCI card (like a GigE or SCSI controller), would be able to physically fit, and continue to function electrically, except at reduced bandwidth, in a PCIe 1x slot. I thought that the same was basically true for PCIe 16x video cards, if you put two into a mobo (with the mobo having two physical 16x or 8x PCIe slots), that each card would run in an 8x mode, which is still 2X faster than AGP 8x is, and bi-directional to boot. (I should double-check my numbers, it might be the same speed, each direction, as AGP 8x is, so when you add the bi-dir nature of PCIe in, it comes out to double the speed.)

I don't know, and probably doubt, that a PCIe 16x video card would function in a PCI 1x slot. Even if it worked electrically, it would probably physically cause that tiny little connector to snap off and destroy the board, considering how much a high-end video-card, with cooler, weighs these days.

Hmm. According to that paper linked to on Dell's site, I'm wrong. I admit, I haven't kept up with the PCIe "revolution", being waiting for the bugs to shake out of it before I even consider upgrading. However, that dell page doesn't even show any physical PCIe 4x cards, nor their notches. According to the pictures, they show a mobo with PCIe 1x slots, and normal PCI slots, side-by-side. I thought that the whole idea of the size of the PCIe 1x connector was so that it could be placed inline with PCI connectors on the mobo, and a card of either type could be plugged into that slot position, for backwards-compatibility purposes?

If neither that, nor the possibility of a higher-spec PCIe card fitting into a lower-spec slot is true, then that doesn't bode well for future multi-mon rigs. In order to run secondary displays, you will have to either have an expensive mobo with "many" PCIe 16x slots, or you will be at the mercy of mfgs to release PCIe 1x lower-end video cards for use as secondaries, and suffer the loss of performance that would come with a scaled-down solution like that.

Perhaps, in the future, much like existing PCI IRQ steering (each PCI slot has four "unique" IRQ lines, A-D), future mobo makers will include a full complement of PCIe "16x" slots, but route the signal lanes to allocate them among the slots, depending on what spec cards you have plugged in. That would allow running multiple PCIe 16x video cards, possibly with each of them getting 4x "lanes" worth of bandwidth.

What a mess. I like the idea of high-bandwidth, point-to-point links, but the whole fracturing of the class of cards between four different connector-size/bandwidth specs, is going to hurt availability of certain configurations of certain types of cards.