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When PC gamers seek motherboards, they focus on numbers such as that of the M.2 slots, USB ports, or even the PCIe slots. Choosing a motherboard for your CPU means you’ll be looking at many boards based on your budget and needs for features and performance. The interesting thing is: any motherboard you buy will have the same amount of currency (given it’s from the same chipset) to spend: the number of PCIe lanes available.

How PCIe lanes work

Powering the board’s I/O

The motherboard gets its PCIe lanes from the chipset (which is built into it) and the CPU. These PCIe lanes connect your CPU to components like the GPU, NVMe drives, and USB devices, transferring data to and from them. Think of PCIe lanes as lanes on a road, more lanes mean more data can be transferred simultaneously between the processor and those components. PCIe links can be x1, x2, x4, x8, and x16 (defining the number of lanes), and PCIe Gen 3, Gen 4, or Gen 5. Each generation doubles the maximum transfer speed, and a PCIe 5.0 x16 link is capable of up to 64 GB/s (per direction) theoretical bandwidth. This is massive; for reference, the fastest Gen 5 M.2 drive is “only” capable of speeds of around 15 GB/s.

Motherboards that use the same chipset and CPU generation will have the same number (and types) of PCIe lanes available to use for I/O. So, you’ll find different motherboards, but they will always have one thing in common: they work with the same number of PCIe lanes. Depending on what segment and consumer the board is aiming for, it will prioritize certain I/O and cut down on others. For instance, a premium board may cut down on the number of M.2 slots for 10G LAN or USB4. Of course, prioritizing certain types of I/O possesses different challenges in terms of cost. For instance, a 10G LAN port is a more expensive addition than a few M.2 slots—due to the network infrastructure required to utilize those speeds.

The bulk of the PCIe lanes in your PC go to the GPU PCIe slot, M.2 slots, and the USB ports. On modern boards, the GPU slot is a x16 linkup, but many boards allow splitting to x8/x8 to share with M.2 slots. The rest of the lanes are occupied by LAN ports, Wi-Fi, SATA ports, and audio.

Lane sharing

When the budget runs tight

Lane sharing is an option on certain boards where you can split bandwidth between certain I/O components. Most commonly, you’ll find this between the secondary M.2 slot(s) and the SATA ports or the secondary PCIe slot(s). Some boards go a bit extreme though, as they try to fit extensive I/O within a limited PCIe lane budget. One recent example of this is the ASRock PG X870 Nova Wi-Fi motherboard, which has 5 M.2 slots. The problem is, three of those share bandwidth with other components, including USB4, SATA ports, and a PCIe slot. This isn’t only limited to this particular board; it’s the chipset’s limitation. Even a $500 X870 motherboard will have the same available bandwidth and must divide it among its connectivity options.

HEDT (high-end desktop CPUs) and their accompanying workstation platform motherboards offer far more PCIe connectivity than standard consumer chips. For example, AMD’s Threadripper 7000 CPUs can provide up to 80 PCIe Gen 5 lanes, and the chipset (TRX50) provides 36 (Gen 4 and Gen 3) lanes. So, the platforms are expensive, but you get plenty of PCIe buying power.

How to manage your lane budget

Ensuring you fulfill your needs

Modern PCs are no longer dominated by a single bandwidth-hungry component like the GPU, but a multitude of additional devices, including NVMe drives and LAN add-in cards. Fortunately, managing the lane budget is simple for the average user, as about every board ensures the basic needs are covered: one x16 GPU PCIe slot, one primary (Gen 4 or Gen 5) M.2 slot, and a variety of USB ports. However, if you plan on using multiple devices, drives, and add-on cards, you should ensure that your motherboard isn’t using lane sharing between the components that you want running at full speed.

Another case that should be considered is bifurcation. If you plan on adding an M.2 add-on card to your motherboard because your storage requirements aren’t being met, your motherboard has to support bifurcation (x4/x4/x4/x4 or x8/x8) for the spare PCIe slot. This will allow you to run expansion cards that add four or two NVMe drives, respectively.

Don’t just focus on I/O—the number of PCIe lanes matter

The motherboard houses all your components and manages communication between them. This is possible through “buses,” with the major one being PCIe. With the number of PCIe lanes on a motherboard being finite, so is the budget for all the devices that the PCIe lanes handle. When considering a motherboard, it’s important to not only focus on how many M.2 or PCIe slots it has, but also how it achieves them—as there might be bandwidth limitations/sharing that, otherwise, you’ll realize only when you experience it.