Will PCI work in a PCI-X slot?

Before I put a PCI card into a PCI-X slot I wanted to know if anyone knows if this will be compatible. I am pretty sure that it won't run at PCI-X speeds, and throttle back to 33Mhz. I have a special I/O card for a server install, and I don't wish to harm the servers motherboard. Don't ask why don't I put it into one of the PCI slots, there are none. 2 month old Dell Server.
1) Will it fit into the slot?

2) Will it run properly?

Thanks in advance
6 answers Last reply
More about will work slot
  1. "PCI-X is downward compatible to PCI. If a PCI card is inserted into a PCI-X system the system will drop down to PCI level operations. It will not execute PCI-X based operations."

    Source: http://www.techonline.com/community/ed_resource/feature_article/7114

  2. Thank you
  3. PCI-X is backward compatible with PCI 2.0 only, not with PCI 1.0 and 1.1 because the minimum clock speed for PCI-X is 66MHz.
    If your card complies to the PCI 2.0 specification (66MHz) it will fit and work without problems, but if you have a 1.0 or 1.1 card (33MHz) it wont work.

    If the card works and you have real PCI-X 1066 cards on your server, plug the PCI card in a different channel than that of real PCI-X cards: the bus is usually splitted in 2 or 3 channels by PCI-to-PCI bridges, read you mobo manual or read the painting on the PCB to find the channel number.
    If you plug your 66MHz card in the same channel where you have a 133MHz PCI-X card, both will run at 66MHz.
  4. Quote:
    the connectors are not compatible

    They are: maybe you have ont of the 5V cards that effectively have the notch in a different position and PCI-X allows 3.3V cards only.
    If you have a 3.3V 2.0 card it will plug in without any problems in the low 32bit part of the connector.
    I currently have a SATA PCI 2.0 controller plugged in a PCI-X connector of an IBM eSeries e325 and it works without problems since 2 years.
  5. It fits regularly, I see no offset at all because in the e325 there are only PCI-X slots... I never used a mixed PCI/PCI-X board, I just can tell that on that server it fits without problems.
    If you want to read further on this go here:


    Ther former explain clearly the backward compatibility issue end the interchangeability of the cards/connectors (you can do even the opposite, plug a PCI-X card in a PCI slot if it supports at least PCI 2.0)

    I forgotten to tell you this: look closely at the PCI-X slot and you'll notice that there is absolutely no key on the lower 32bit part of the connector, allowing the PCI cards to be inserted.
    On the contrary the key is present in the normal PCI slot, preventing the insertion of very fast PCI-X cards that are not compatible with the PCI standard (essentially fast SCSI controllers, normally the NIC adapter do have the notch and can be inserted in PCI slots)
  6. Quote:
    the connectors are not compatible

    Sow how does it fit with the PCI-x slot being offset from the PCI?

    PCI-X and PCI connectors are compatible, the difference being between the notches for a 3.3v card and a 5v card...the slot is not offset either, not sure what you mean by this...I've plugged in 66MHz PCI-X cards into PCI slots and vice versa with no issues...

    Don't confuse PCI-X with PCIe...
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