Modding a PCI-E 16x card to work in a 1x slot AND in a 16x slot

jmke · 4th August 2005, 23:22

Theory
PCI-E is basically a network protocol over a series of network links. The chipset is the ‘Switch’, the lanes are the ‘cables’ and the cards are the ‘servers’. A single PCI-E slot is made up of one or many lanes. This can be likened to a network trunk. A 1x slot is like a single cable to a server, a 4x is like a 4 cable trunk and a 16x is like a 16 cable trunk. Data to be sent to the card is encapsulated, sent over multiple lanes, and then de-encapsulated once more. Just like a network trunk.

Again like a network, I recall the PCI-E specification saying that devices can negotiate for lanes and what speed the lanes run at. The speed, I assume is for future compatibility when they up the PCI-E speed to 200mhz or something, and the negotiation should mean that if a lane is faulty or missing or reassigned elsewhere (as it is in SLI) that the device can just keep on going with less available bandwidth.

We’ve already seen an example of its adaptability with SLI. With SLI, there are 2 physical 16x PCI-E slots. Under non-SLI configuration, one slot runs with 16 lanes and the other with 1 or 2 (that’s up to the motherboard manufacturer). When the key or bios setting is changed, the first slot loses 8 lanes. They are physically re-routed (either with a physical key or an electronic switch) to the second port. In this mode, the first card runs 8 lanes and the second card runs 8 lanes. There have also been reports of cards working in open ended 1x and 4x slots.

http://www.overclockers.com.au/article.php?id=395983

4th August 2005, 23:22	#1
jmke Madshrimp Join Date: May 2002 Location: 7090/Belgium Posts: 79,022	Modding a PCI-E 16x card to work in a 1x slot AND in a 16x slot Theory PCI-E is basically a network protocol over a series of network links. The chipset is the ‘Switch’, the lanes are the ‘cables’ and the cards are the ‘servers’. A single PCI-E slot is made up of one or many lanes. This can be likened to a network trunk. A 1x slot is like a single cable to a server, a 4x is like a 4 cable trunk and a 16x is like a 16 cable trunk. Data to be sent to the card is encapsulated, sent over multiple lanes, and then de-encapsulated once more. Just like a network trunk. Again like a network, I recall the PCI-E specification saying that devices can negotiate for lanes and what speed the lanes run at. The speed, I assume is for future compatibility when they up the PCI-E speed to 200mhz or something, and the negotiation should mean that if a lane is faulty or missing or reassigned elsewhere (as it is in SLI) that the device can just keep on going with less available bandwidth. We’ve already seen an example of its adaptability with SLI. With SLI, there are 2 physical 16x PCI-E slots. Under non-SLI configuration, one slot runs with 16 lanes and the other with 1 or 2 (that’s up to the motherboard manufacturer). When the key or bios setting is changed, the first slot loses 8 lanes. They are physically re-routed (either with a physical key or an electronic switch) to the second port. In this mode, the first card runs 8 lanes and the second card runs 8 lanes. There have also been reports of cards working in open ended 1x and 4x slots. http://www.overclockers.com.au/article.php?id=395983 __________________