The amount of PCIe express lanes you need depends upon the amount and the type of expansion cards you plan to install.
In the following text I explain in detail what PCIe lanes are. the type of expansion cards out their and their lane requirements in an attempt to answer the query: how many PCIe express lanes do I need.
It is important to gauge the overall lane requirement for your system because the amount of PCIe lanes a certain PC has are limited.
The amount of PCIe lanes you have depends upon your CPU make and model as well as on your motherboard chipset.
For instance, a typical Intel Core series processors from 10th generation and below offers 16 PCIe lanes and a typical AMD Ryzen processors offers 24 PCIe lanes.
However, not all lanes provided by the CPU or the motherboard chipset can be user accessible. Meaning, not all lanes connect to a PCIe slot for putting an expansion card into.
We will explore this topic in detail below
PCIe Lanes, CPU and Chipset in Brief
PCIe lanes are the primary network that transmit information to and fro the connected expansion cards on the PCIe slots to the CPU. Think of these as pipelines or highways that facilitate the flow of information on your PC.
Now the amount of PCIe lanes you have on your system are limited in number. Your CPU and the motherboard chipset defines the amount of PCIe lanes you have.
As mentioned earlier, a typical AMD Ryzen series processor offers 24 PCIe lanes However, not all lanes provided by a typical Ryzen CPU are user accessible in the form of a PCIe slots.
Four of these lanes are used up by other components like an M.2 slot, four more connect to the motherboard chipset through a downlink for powering it and as a result, only 16 are available from the CPU for the expansion slots.
The 16 user accessible PCIe lanes are primarily in the shape of an x16 slot for installing a graphics card into.
In addition to CPU, the motherboard also offers PCIe lanes (aka HSIO lanes). The amount of lanes the motherboard offers depends upon the type of chipset it features.
For instance, a low end AMD A520 chipset offers 6 PCIe lanes, AMD B550 offers 10 and the premium AMD X570 offers 16 PCIe lanes.
Following are some of the chipsets and their corresponding PCIe lane count.
|B460||16||Mid Range /
|B560||12||Mid Range /
Configuration of PCIe Lanes
The following graphic illustrates how the CPU and Motherboard chipset (AMD B550) lanes are configured:
On the left hand side you can see the how the 24 PCIe lanes of the CPU are configured. On the right hand side (on the far right blue boxes), you can see the B550 chipset offering a configuration of 10 PCIe lanes.
Again, not all motherboard chipset lanes are user accessible. Some of these are connected to built in devices like an onboard Ethernet card, SATA slots, sound card etc.
Often you will find x4 and a x1 PCIe slots originating from the motherboard chipset.
If you want to learn more about about how many PCIe lanes you have, we recommend giving this article a read.
The important point to take note of here is that the PCIe lanes you have are FINITE in number.
So How Many PCIe Express Lanes Do I Need?
Well that depends entirely upon your PC configuration and what kind of expansion cards you have.
Different expansion cards have a different lane requirements. Demanding expansion cards require a higher number of lanes compared to weaker cards like WiFi Network cards.
Graphics Cards PCIe Lane Requirement
A graphics card is designed to use 16 PCIe lanes ideally originating from the CPU. If you have a single graphics card, you would connect this to the top PCIe x16 slot located on your motherboard.
The top PCIe slot has 16 PCIe lanes connected to the CPU.
Now if you have two Graphics Cards, you cannot possibly assign 32 PCIe lanes to them on a typical PC. A typical PC may only have about 20 user accessible PCIe lanes in total.
Hence, if you have two graphics card, and two PCIe x16 slots, the lanes get divided into x8/x8. Often, the difference between running a graphics card in x8 mode instead of x16 is quite marginal.
But it is worth noting that NVIDIA Graphics cards require atleast an x8 slot to work. AMD Graphics cards, on the other hand, can also work on x4 slots i.e on lower bandwidth slots.
Consider the motherboard above. This is a motherboard designed for NVIDIA SLI configuration. It has two x16 slots and they work in the following configuration x16/0 and x8/x8.
Meaning, if you occupy the first slot, it will utilize all 16 lanes. If you occupy the second slot, the lane width gets divided between the two slots.
So having two PCIe x16 slots does not mean you have 32 PCIe lanes!
It is worth learning more about PCIe slots here as well as about GPU and their lane requirements more in depth here:
- Does it Matter Which PCIe x16 Slot I Use?
- How to Check How Many adn Type PCIe Slots You Have?
- How Many PCIe Lanes Does a GPU Use?
So, the main point to note down here is that Graphics Cards take up 16 lanes.
The Rest of The Cards and Their Lane Requirements
As for the rest of the cards, the PCIe lane requirement is variable.
For instance, an Ethernet Network Card may require one lane if it has 1 Gbps bandwidh, or 4 lanes if it has 10 Gbps bandwidth (these are known as 10G cards).
Similarly, a video capture card may require either 1 PCIe lane or four depending upon whether it is an FHD video capture card or a 4k video capture card.
We talk in depth about all the popular expansion cards and their lane requirements here:
The following table should also help,
Summary of Expansion Cards and Their PCIe Lane Requirements
|Card||PCIe Lane |
|NVIDIA Graphics Card||16 or 8||16 ideally
8 in case of SLI
|AMD Graphics Card||16, 8, or 4||16 ideally
8 or 4 in case of crossfire
|Ethernet Network Card||1 or 4||1 in case of 1 Gbps (v3.0)
4 in case of 10 Gbps (v3.0)
|WiFi Network Card||1|
|Video Capture Card||1 or 4||1 in case of 1080 capture (v3.0)
4 in case of 4k capture (v3.0)
|SATA Expansion and|
|1, 4, 8||The lane requirement depends upon number of SATA slots, and whether it has RAID Controller|
|M.2 NVMe Expansion Card||4|
|TV Tuner Cards||1|
|Port Expansion Card||1 or 4||Depending upon the type and number of port. Thunderbolt 3.0 port, for instance, requires 4 PCIe Lanes (v3.0)|
|Riser/Splitter||1, 4, 8, 16|
Adding Up the Total PCIe Lanes Occupied by Cards
In the end, once you have taken note of all the expansion cards and their lane requirement, you can figure out how many PCIe lanes you need in total.
The number should be equal to or less than the total amount of PCIe lanes you have.
So for instance, if you have 20 PCIe lanes on your system and you install a Graphics Card (16 lanes), an M.2 SSD Expansion Card (4 lanes), and also a 1G Ethernet Card (1 lane), then one of the component will get disabled.
So while you may still have more slots than you have PCIe lanes available to you, you have to be careful and read the motherboard manual and spec sheet. This particularly happens when you have slots sharing PCIe lanes.
Slots Sharing PCIe Lanes
The amount of PCIe slots you have do not always correspond to the amount of lanes you have. This is particularly true when slots share PCIe lanes.
Take MSI B550-A Pro motherboard for instance.
On this motherboard, the PCIe x16 (x4) slot shares PCIe lanes with the M.2 slot. So when either is occupied, the other would get disabled.
PCIe lanes are limited. As such, knowing how many PCI Express lanes do I need can come in handy when making a purchasing decision or deciding on which cards to install.
Different cards use different numbers of lanes and the sweet spot is finding a CPU and a motherboard that can accommodate that number.