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PCI-X Backwards Compatible?

P

Phaethar

Weaksauce
Joined
Dec 13, 2002
Messages
92
Hey all,

Just had a quick question about PCI-X.. I've installed some 64-bit cards into older, 32-bit PCI slots, but not the other way around. Will 32-bit PCI cards still work in 64-bit slots? I'm guessing that they would, but I wanted to make sure before I picked up a board that used them and then found out that my hardware won't work. Thanks.
 
As long as they're keyed correctly, they should. Beware, though, they'll drop the speed of the bus down to 32/33.

What board are you looking at?
 
Yep, they'll work just fine. But also, PCI-X != 64bit PCI slot. PCI-X is like a dedicated line to a PCI slot that works at IIRC 133mhz. But regardless, you'll still be fine
 
Originally posted by Vertigo Acid
Yep, they'll work just fine. But also, PCI-X != 64bit PCI slot. PCI-X is like a dedicated line to a PCI slot that works at IIRC 133mhz. But regardless, you'll still be fine
Click to expand...
Ehh.

I'm pretty sure all PCI-X busses are 64 bits wide. There are quite a few boards out there with two 100MHz slots on one bus and one 133MHz slot on another, plus a couple of 33MHz 32-bit PCI slots for legacy support.
 
The PCIe is backwards compatible, but the actual slots themselves will probably not. The reason for this is that if you do put a PCI (33MHZ) card on the bus, then the entire PCIe bus will drop down to that speed.

What will probably happen is that there will be multiple busses that the MB will have. 1 PCIe bus dedicated directly the graphics card. 1 PCIe bus dedicated to probably 2 or 3 expansion slots. And a final regular PCI bus dedicated to 2 or 3 regular pci slots.

The real neat part of this will be the ability to have multiple kickass graphics cards, for multi-monitor setups. No more having to rely on crappy PCI cards.
 
Thanks for all the info on this. I'll try to summarize why I'm looking at this.. Basically, I'm trying to put together a 2U rack mountable box using some existing parts. Those parts include a P4 2Ghz (Northwood), 2GB of DDR ECC RAM, a 64-bit ATA RAID card, and a 32-bit UW SCSI card that needs to be accessible by external devices (tape drive).

I'm looking at a couple of Supermicro boards (the P4SCi and the P4SCT+II), both of which NewEgg carries of course.

What I'd like to do is put in the board, then use a 64-bit riser card in the first PCIe slot. Then I would like to install the RAID card and the SCSI card in the riser. If that means that the RAID card would have to run as a 32-bit card, then I'll have to live with that. As long as it all works. ;)
 
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