Learn about the PLX and PCH chip and how they assign PCIe Lanes
Episode #12-06 released on October 1, 2021
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Each processor has a set amount of PCIe lanes that it was designed with. These lanes are used by a variety of hardware in your computer, both aftermarket and built into your mainboard.
Your mainboard may be developed to support a certain number of lanes from the CPU, and the amount available will depend on the supported CPUs. Your mainboard may, also, include PCH chips and PLX chips, both of which can assign PCIe lanes.
The PLX chip will assign CPU bound PCIe lanes, typically to the GPU itself, and PCH lanes, which are slower and can only be assign in 4 PCIe lane chucks are slower and usually reserved for things like drives, networking, etc. These are rarely used by graphics because Nvidia requires a minimum of 8 PCIe lanes for each graphics card. This usually means that the PCIe lanes typically reserved for graphics, are using PCIe lanes provided by the CPU itself, and the rest are being supplied by the onboard PCH chipset.
PCH chips can only be assigned PCIe lanes in chunks of 4, and this means that regardless of the number of PCIe lanes available from the onboard PCH chip, you can only realistically connect a set number of devices, which would equate to the total number of PCH lanes divided by 4. If only 24 lanes are available to PCH chip, then only 6 devices would be available. And some of these lanes are already assigned to onboard hardware, too. It is important to note that the PCH initially was released on the Intel platform in 2009. Mainboards before this time were using different technology and resulted in lower performing computers.
The combination of the PLX and PCH chips on a mainboard with the included lanes provided by the CPU manufacture and mainboard manufacture allows everyone to customize their computer in a way that allows anyone to complete the tasks they need to achieve and enjoy all the multimedia and games they desire. This means that you can easily use more lanes than the Processor provides, but it is possible, because of PLX chips, to be using fewer lanes than you actually think, example is SLi.
SLi is a Nvidia technology and allows multiple graphics cards to work together. It requires at least 8 PCIe lanes per card. If you processor has 32 lanes and you have 3 graphics card in SLi, you would think that you were using 16 per card and calculate a total of 48, when you are likely only using 24 lanes, 8 per graphics card. You could run a two graphics card setup at 16 PCIe lanes each if you have at least 32 CPU bound PCIe lanes.
That being said, with the advancements of graphics cards and the increase speeds in PCIe with the fourth generation, you do not need to use more than 8 PCIe lanes, because there is so much available bandwidth.
And, now you know why you can use more PCIe lanes than your processor ships with, and it is all because of PLX and PCH chips.
Host : Steve Smith | Music : | Editor : Steve Smith | Producer : Zed Axis Dot Net