Hope this isn't too off-forum, or too clueless for that matter...
I bought off eBay an intem which was billed as:
"IBM X346 Server Dual PCI-X Riser Card 13M7656AA 26K4762"
It looked an awul lot as if it had a PCI-e x16 edge connector, on a PCB fitted with some sort of heatsinked chip, and a couple of PCI-X slots. I realise it wasn't billed as a PCI-e to PCI-X adapter card, but I thought I'd give a go, as I have some PCI-X RAID cards I'd quite like to use. I used a known-working PCI-e x16 cabled riser card (tested to work with my graphics card) to connect this new card to two PCs (an old Dell Optiplex GX620, and a home-made box with a Gigabyte P43 board and Intel E6600). Niether machine would boot at all (wouldn't even power up) with the IBM riser card in it, despite the fact that the edge connector is a perfect fit in a PCI-e x16 slot, and the pin spacing is identical.
I know that the use of a particular socket for this sort of card (intended for server use) doesn't guarantee that it will be universally usable in a x16 PCI-e slot, so I'm wondering if anyone can tell me definitively if these sorts of cards are indeed usable only in the servers for which they were originally designed, or if I've got a duff card.
OK, tried a second card (this time an HP), and this burned through three of the traces on the cabled PCIe extender/riser, and produced the unmistakable smell of burning silicon from my PSU, so - not compatible! Shame, would have been handy..