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PCIe 16x to 8x This article engages in the modification of an 16x PCI-Express card to make it operable in an 8x socket. PCI-Express cards are, according to electrical transmission, downwards compatible. Hence it is possible to plug a 16x card into an 8x socket. The card will then run at 8x speed. But there are PCIe sockets with different length and a long card does not fit mechanically into a short socket, although the card (if it would fit) could automatically switch to the coressponding lower speed. Larger sockets can take up smaller card but not the other way.

There are different electrical speeds defined for PCI-Express cards: 1x, 2x, 4x, 8x and 16x. The demand for electrical conections (lanes) grows with the speed of the card. The number of plug contacts increase along with the cards speed. The common contact pins that every card needs, e.g. for its power supply, are in direction of the faceplate. Afterwards a notch follows and thereafter the plug contacts for the lanes. Indeed the card does not necessarily need all lanes. The card switches to the next lower speed if the backward lying lanes are not connected.

There are sockets with a different number of pins consistent with the plug contacts on the card. There are sockets with 36 (1x), 64 (2x and 4x), 98 (8x) and 164 (16x) pins. In fact the mainboard manufacturers could equip all systems with 164 pin sockets, even if they make use of lesser lanes. In this case all cards would fit into the socket and simply switch to the speed, that would be possible by the actually number of connected lanes. Unfortunately some manufacturer make use of shorter sockets and cards with 164 contacts do not fit in these. Some manufacturers are cruel enough to to equip 164 pin sockets which they barricade with an across lying divider, so that only shorter cards will fit.

Now the problem is that cheap PCI-Express graphic cards are almost always offered as 16x types with 164 plug contacts. With a little courage and some tools one can operate these cards in short or blocked socket. Here is how it works:

Use an adapter There are adapters available who lengthen the socket. But they raise the assembly height by a few millimeters, so that the computers housing can not be closed any more. And actually they cost round about as much as a cheap graphics card.

Mill out the socket It is possible to mill out the end of a short socket. The exessive pins of the card will simply hang out of the socket. The maliciously assembled dividers can be cut or milled out as well. There are some people who where successfull with hot blades, Proxxons and other tools. Recommended for cheap mainboards and expensive cards.

File a notch in card Since I feard to damage my Intel SE7320SP2 board I preferred to file a notch into my 29 € GigaByte Radeon HD 2400 XT. This had worked. I filed in the notch with a small needle file. First you have to know where the notch has to be placed. The card has the half of all plug contacts located on each side. If you have an 98 pin socket (8x) there are (98 divided by 2) 49 contacts on each side of the card. Contact No. 50 will only be needed for the next larger (164 pins / 16x) socket. This one and all following ones (away from the faceplate in direction of the cards end) could be filed off. But a small slot at this position suffices. The right pin can be counted and marked:

Unfortunately I miscounted, marked pin No. 49 on my card and sacrificed it to my file. Now my card runs only with the next lower speed 4x. In my case this was no problem because the manufacturer contacted my 98 pin socket with only 4x lanes. Be careful during the filing that no copper splinters remain who might cause short circuits between the conductor pathes. It is advisable to wrap a copper wire from a cable around your wrist, the file and the faceplate of the card so that everything has the same electrical potential and ESD damages can not occur. The result after five minutes of work looks like this:

Afterwards the card fits into the shorter 98 pin socket and switches automatically to the corresponding speed:

This operation might not work with all cards and in the end the card could be broken. Possibly some conductor pathes might hide inside the card between the plug contacts. If those are cut through the card is on the blink. Indeed an operation at the socket could be risky as well. Pins could get damaged during the milling, bending and cutting. If an ESD damage is caused here it might impact the mainboards I/O controller. Conclusion: Only for craftsmen who have strong nerves.