Small motherboards in the compact Micro-ATX and Mini-ITX formats rarely have more than two PCI express slots. The usual equipment on Micro-ATX boards usually includes two short slots for PCI-Express x1 and a long slot for PCI-Express x16, which is intended for a graphics card. What to do if a PCI Express card according to the standard x4 or x8 does not fit into the short or long slot?

In general, shorter PCI Express cards also work in longer slots. The terms x1, x4, x8 and x16 indicate the number of lanes and thus the number of plug contacts of the slot. The PCI Express standard is backwards compatible. That is, a card with x4 also fits into one for x8 and x16 slot and then simply uses correspondingly less of the lanes available there.

Conversely, PCI-Express is not so lenient when operating multi-lanes on short slots: It is true that the standard is to negotiate the number of lanes used at the time of the boat with a card.

But purely mechanically, longer PCI Express cards just don’t fit into shorter slots. Even the firmware or bios of the main board will not reliably detect larger cards, even if you open a 1x slot on a page with a file.

Exceptions: Occasionally there are motherboards whose 1x slot has already remained open from the manufacturer on one side in order to pick up longer cards. With these boards, it should also work on the part of the bios or firmware to operate PCI Express cards at a slower speed and less lanes. A helpful tool in the command line when experimenting with PCI Express cards is lspci:

Lspci
The command displays the detected PCI hardware.

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