Can I fit a PCI expansion card into a different type of slot?

This content is 16 years old. I don't routinely update old blog posts as they are only intended to represent a view at a particular point in time. Please be warned that the information here may be out of date.

The new server that I bought recently has a huge case with loads of room for expansion and that got me thinking about all which components I already had that I could reuse.  DVD±RW dual layer recorder from the old PC, 500GB SATA hard disk from my external drive (swapped for the 250GB disk supplied with the server), couple of extra NICs… "oh, hang on.  Those NICs look like PCI cards and I can only see a single PCI slot.  Ah!".

I decided to RTFM and, according to the technical specifications, my server has 5 IO slots (all full-height, full length) as follows:

  • 2 x 64-bit 133MHz PCI-X
  • 1 x PCIe
  • 1 x 8 PCIe
  • 1 x 32-bit 33MHz legacy slot

I knew that the spare NICs I had were PCI cards but would they fit in a PCI-X slot?  Yes, as it happens.

I found a really useful article about avoiding PCI problems that explained to me the differences between various peripheral component interconnect (PCI) card formats and it turned out not to be as big an issue as I first thought.  It seems that the PCI specification allows for two signalling voltages (3.3v and 5v) as well as different bus widths (32- or 64-bit).  32-bit cards have 124 pins whilst 64-bit cards have 184 pins; however to indicate which signalling voltage is supported, notches are used at different points on the card – 5V cards have the notch at pin positions 50 and 51 whilst 3.3V cards have the notch closer to the backplate at pin positions 12 and 13.  Furthermore, some cards (like the NICs I wanted to use)Universal PCI card have notches in both positions (known as universal cards), indicating that they will work at either signalling voltage.  Meanwhile, PCI-X (PCI eXtended) is a development of PCI and, whilst offering higher speeds and a longer, 64-bit, connection slot, is also backwards-compatible with PCI cards allowing me to use my universal PCI card in a PCI-X slot (albeit slowing the whole bus down to 32-bit 33MHz).  PCIe (PCI Express) is a different standard, with a radically different connector and a serial (switched) architecture (HowStuffWorks has a great explanation of this).  My system has a single lane (1x) and an 8-lane (8x) connector, but 1x and 4x PCIe cards will work in the 8x slot.

PCI slotsThis illustration shows the various slot types on my motherboard, an 8x PCIe at the top, then a 1x PCIe, two 64-bit PCI-X slots and, finally, one legacy 32-bit 5V PCI slot.

After adding the extra NICs (one in the 32-bit legacy 33MHz slot and the other in one of the PCI-X slots) everything seemed to fit without resorting to the use of heavy tools and when I switched on the computer it seemed to boot up normally, without any pops, bangs or a puffs of smoke.  All that was needed was to get some drivers for Windows Server 2008 (these are old 100Mbps cards that have been sitting in my "box of PC bits" for a long time now).  Windows Device Manager reported the vendor and device IDs as 8086 and 1229 respectively (I already knew from the first half of the MAC address that these were Intel NICs), from which I could track down the vendor and device details and find that device 1229 is an 82550/1/7/8/9 EtherExpress PRO/100(B) Ethernet Adapter.  Despite this being a discontinued product, searching the Intel Download Center turned up a suitable Windows Vista (64-bit) driver that was backwards compatible with the Intel 82550 Fast Ethernet Controller and I soon had the NICs up and running in Windows Server 2008, reporting themselves as Intel PRO/100+ Management Adapters (including various custom property pages provided by Intel for teaming, VLAN support, link speed, power management and boot options).

So, it seems that, despite the variety of formats, not having exactly the right PCI slot is not necessarily an issue.  PCI Express is an entirely different issue but, for now, my 32-bit universal PCI card is working fine in a 64-bit PCI-X slot.

3 thoughts on “Can I fit a PCI expansion card into a different type of slot?

  1. any help would be appreciated. I have an eight years old motherboard and want to fit my new fast ethernet into the pci slot. The card fits into the slot. The large side of the ethernet is a perfect fit. But the small part of the ethernet pci connetor seems smaller than the part of the pci slot it fits into. Will the ethernet card work if this is the case or will the voltages be different or some other problems?


  2. Ok, so 32bit PCI cards can run in 64bit PCI slots…but can a 64bit universal PCI card run in a 32bit PCI slot?

  3. Alan, Eric – sorry, but the short answer is that I do not know. In the case of 64-bit card running in a 32-bit slot, I doubt it as the card is unlikely to know that it can only use part of the bus, but I may be wrong.

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