The motherboard is a complex component that should be considered carefully for many reasons, one of those reasons are PCIE lanes.
Many builders will overlook the importance of PCIE lanes, you should always have in the back of your head the number of PCIE lanes you want as this makes upgrading your PC significantly easier.
A PC consists of, PCIE lanes from both the motherboard chipset and the CPU. The CPU lanes are reserved for the x16 graphics card slot, and the chipset lanes are reserved for onboard USB ect.
CPU Lanes Vs Chipset Lanes Main Differences
The key difference between CPU and chipset lanes is that the CPU lanes are primarily used by the graphics card, and it’s a low latency solution for high bandwidth components.
The GPU uses the x16 PCIE lanes run by the CPU because it introduces less latency compared to the chipset PCIE lanes.
The chipset lanes are primarily used for low-bandwidth components such as USB, Ethernet, M.2, Audio, Firmware, and SATA.
These devices that use the PCIE lanes don’t need the fast latency that the CPU provides, so it’s not a big deal to have them bottlenecked by the chipset lanes.
Chipset’s Limited Bandwidth Can Hurt GPUs
Using the graphics card on the chipset lanes can be a big issue due to the huge bandwidth bottleneck. The chipset is limited by a 4-lane PCIE cap which means high-performing components won’t work as fast.
Also consider that the chipset lanes are being used up by many other components such as the USB, Ethernet, and SATA which can impose an even bigger bottleneck.
Also Read: Which Slot For GPU?
The Number Of Chipset Lanes Vary On The Type Of Chipset
Some chipsets will come with more PCIE lanes than others, usually, the higher-end motherboards will come with a higher number of PCIE lanes.
More affordable boards will come with fewer PCIE lanes which means affordable boards will often offer fewer options for upgradability.
To check how many PCIE lanes your motherboard comes with, the easier way is to check the motherboard manufacturer’s website or the manual.
However, here’s a table showcasing how different chipsets have a different number of PCIE lanes.
| Motherboard Chipset | Number Of PCIE Chipset Lanes | Type Of Board |
|---|---|---|
| Intel Z690 | 28 | High Performance |
| Intel W680 | 28 | High Performance |
| Intel H670 | 24 | High Performance (No OC) |
| Intel Q670 | 24 | High Performance (No OC) |
| Intel H610E | 12 | Budget Performance |
| Intel H610 | 12 | Budget Performance |
| Intel B660 | 14 | Mid Range |
| AMD X570 | 16 | Mid Range |
| AMD B550 | 10 | Budget Performance |
| AMD A520 | 6 | Budget Performance |
The Number Of CPU Lanes Vary On The CPU Generation
The number of PCIE lanes that comes with a processor isn’t tied to the CPU specifically, it’s tied to the microarchitecture of the CPU itself.
So every processor in the same generation will have the same number of PCIE lanes with some exceptions, mobile processors will typically come with fewer lanes.
And HEDT processors will come with a ton more PCIE lanes, for example, the Threadripper processors will usually come with 64 or more PCIE lanes.
And some pro model Threadrippers such as the Ryzen Threadripper Pro 3995WX will come with 128 PCIE lanes, so there are some exceptions to the rule.
| CPU Generation | Number Of PCIE Processor Lanes | PCIE Version |
|---|---|---|
| Intel 12th Gen/Alder Lake | 20 | 2022 |
| Intel 11th Gen/Rocket Lake | 20 | 2021 |
| Intel 10th Gen/Comet Lake | 16 | 2019 |
| Intel 9th Gen/Coffee Lake | 16 | 2017 |
| Ryzen 5000 | 24 | 2020 |
| Ryzen 3000 | 24 | 2019 |
| Ryzen 1000 | 24 | 2017 |
Long PCIE x16 Connector Uses CPU Lanes
You really shouldn’t have to worry about using the wrong PCIE lanes for your graphics card as the long PCIE x16 slots are typically connected to the CPU.
The problem is that the 2 or more x16 PCIE slots will share the exact same x16 PCIE lanes that are connected to the CPU, so you can’t have two graphics cards running at full speed.
As long as your CPU comes with 16 or more PCIE lanes, the x16 slot should run at full bandwidth. So if your CPU only has 8 lanes, your GPU will run at half the bandwidth.
Most CPUs today will come with at least 16 PCIE lanes, and they’re only increasing per CPU generation; you can find CPUs with up to 20 PCIE lanes.
Your M.2 Drives Should Use CPU PCIE Lanes
There are some exceptions, but the processor lanes are generally allocated toward the x16 slot for the GPU, and 4 lanes should be reserved for the M.2 drives.
Motherboards that allow M.2 drives to use CPU lanes are significantly faster as they aren’t bottlenecked by the chipset. They can move more data freely.
Secondary M.2, and other storage drives will use lanes from the chipset as the 4 lanes provided by the processor are already used up by the primary M.2 drive.
And the chipset will transfer data by its own dedicated 4 lane PCIE bus which inhibits a bottleneck and latency to devices connected to the chipset lanes.
So all devices using the chipset lanes will have a cap on their performance due to the 4-lane PCIE bus.
Make Sure The Slots You Use Are Connected To CPU Lanes
When choosing a motherboard, you should always have this in mind, always ensure that the PCIE slots you plan on using have the CPU lanes allocated to them.
This ensures you get the maximum performance out of the devices you plan on using frequently, PCIE Chipset lanes are great for devices that aren’t used consistently and don’t move a lot of data.
Also when installing the graphics card, always use the top slot, this is because the top slot will always use the CPU lanes, or consult the motherboard’s manual to be 100% sure.
Another tip, if you’re installing extra PCIE components into your computer, be sure to use the right slot as that can impose a limit on your graphics card.
This is because your motherboard will usually have two slots that share the x16 lane coming from the processor, always reserve these slots for high-speed components such as graphics cards.
Also Read: Does Motherboard Affect Performance?
Conclusion
In conclusion, the CPU lanes have higher bandwidth and lower latency because of the direct connection to the CPU.
Chipset lanes have less bandwidth and higher latency, this is perfect for USB, SATA, and Audio devices, this is because they don’t need a lot of bandwidth.
Basically, just ensure that you’re using the right PCIE lanes so you can get the most out of your system, the GPU should always have a direct connection with the CPU, and other components that are less important can use chipset lanes.
