PCI/PCI-X Compatibility?

[TimP]

I'm thinking about putting a SCSI card in a small form factor PC I'm building which only has PCI slots. Most Ultra160 SCSI cards I've seen are PCI-X, though. My initial thoughts are that you cannot put PCI-X cards in PCI slots, however on several cards I've seen statements like this: "Uses the latest 64Bit / 66Mhz PCI interface (32-bit compatible)". Does that mean it's compatible with standard PCI slots or is it some sort of PCI-X backwards compatibility mode so it's compatible with the operating system? I know that the PCI-X bus has much more bandwidth than standard PCI which would degrade performance a bit.

Thanks,
Tim

 

[Captain Slug]

PCI-X slots/cards are backwards compatible, if the card you're installing is stated as also being backwards compatible it will work.
If the card does not, then it will not be.

It just has to indicate that it's meant for PCI-X and PCI usage.

The opposite however is not true as far as I know. A regular PCI card is not forward-compatible with PCI-X. Which explains why even the newest boards still include standard PCI slots. If I'm not corrent on this portion someone can correct me but it's what I've been able to deduce from what little I've seen.

 

[TimP]

I did some searching on Google and found this on HP's site:

Q. Will new PCI-X cards be compatible in conventional PCI based systems?
A. Yes, PCI-X cards can be used in a conventional PCI system. PCI-X is backwards compatible with conventional PCI products, which allows existing PCI-X cards to operate within a PCI environment. However, the PCI-X card will default to the speed of the PCI bus (either 33 MHz or 66 MHz).

It sounds like all PCI-X cards are backwards compatible. Can anyone back this claim up? The Q&A seems like marketing material so I want to make sure this is a fact and not idealistic sales BS.

 

[Captain Slug]

It sounds like all PCI-X cards are backwards compatible.

The specification says they should be, but not all the cards available now are meeting the specification 100% in this regard. I have yet to see any indication that PCI-X video cards are at all usable in older PCI slots.