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How can a PCI-E x1 card require x4 slot?

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December 5, 2010 9:17:41 PM

I am setting up a SAN that will be consumed by various PCs including a HTPC. For the SAN I picked up one of these:

http://www.intel.com/Assets/PDF/prodbrief/pro1000_pt_du...

It is an Intel Pro/1000 PT dual-port NIC. The card is in a PCI-E x1 card but when reading the data-sheet it says that it requires a x4 slot.

Quote:
Compatible with x4, x8, and x16 full-height
• Allows dual-port operation in almost any PCI Express server slot, except x1 slots, PCI Express slots and allows each port to operate without interfering with the other


The above is quoted from the linked data-sheet towards the bottom of page 1.

To me this doesn't make sense, I thought the various PCI-E form-factors, e.g. x1, x4, x16, indicated how many lanes. So I don't understand how a card that is PCI-E, meaning it has 1 lane, requires a x4 slot, 4 lanes. It doesn't have physical connections to use the additional lanes does it?

My main problem is my motherboard has 1x PCI-E x16 and 2x PCI-E x1 slots. I require the PCI-E x16 for my Ceton InfiniTV card. My only other option is 2x Intel Pro/1000 PT single-port or some other quality server card.

More about : pci card require slot

December 5, 2010 9:54:22 PM

You're confusing the PCI Express expansion card bus version number 1.0a with the card's physical bus and slot size of ×4 lanes.

A PCIe card will physically fit (and work correctly) in any slot that is at least as large as it is (e.g., an ×1 sized card will work in any sized slot).

In your case your x4 sized card is physically impossible to fit into an x1 sized slot but it will fit and work in an x4 or x8 or x16 sized slot.

Isn't the Ceton InfiniTV card an x1 sized card? You said your motherboard has 2x PCI-E x1 slots so why can't use one of those for the TV card?
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December 5, 2010 10:11:29 PM

You are right that the Ceton IniniTV card is a x1 so my problem may be resolved but I am definitely not mistaking the specification version for the lanes, if you read the data-sheet it specifically states it is compatible with x4, x8 and x16.

Even though my problem may be resolved I am curious how a x1 card can require a x4 slot or even use an x4 slot more effectively than an x1 slot.
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December 5, 2010 10:28:21 PM

I found my answer, quoted from the following document:

http://www.intel.com/Assets/PDF/whitepaper/mesh_pcie_wh...

Quote:
As per the PCI Express specification, lanes via add-in slots
can be implemented as x1, x4, x8 or x16 lanes. This allows
designers to scale up the PCI Express serial bus I/O
frequency to as high as 64 Gbps (see Table 1) by adding
lanes to PCI Express cards and computer slots. For example,
a x1 lane provides adequate bus bandwidth for the PCI
Express I/O of the Intel® PRO/1000 PT Server Adapter.
However, to provide additional I/O bandwidth for a dual-port
Gigabit Ethernet adapter, a x4 lane is used in the Intel®
PRO/1000 PT Dual Port Server Adapter.
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