What are PCIe Lanes?
PCIe lanes refer to the physical link between the processor or chipset and the devices that support PCI Express. Technically, a PCIe lane is a set of two pairs of copper wires. These are called traces or signal traces and run through the motherboard.
- PCI Express lanes signify the physical link between the processor or chipset and the devices that support PCI Express.
- PCIe lanes comprise two pairs of copper wires, commonly called the traces, running through the motherboard and connecting the PCIe supported devices to the motherboard chipset or the processor.
- There can be up to 32 bi-directional PCI Express lanes in a single device that supports high bandwidth and higher transfer rate of data.
Understanding PCIe Lanes
PCIe lanes, also known as PCI Express lanes, are the signal traces on the motherboard.
In every lane there are two wires dedicated to send data and two separate wires dedicated to receive data.
This separation offers full bandwidth support that can be used in both directions at the same time.
The PCI Express lanes play a crucial role in the overall performance of the computer and its components and therefore should not be taken lightly at all.
If it is right in type and number, it will future proof your machine thereby reducing the need for upgrading it frequently down the road.
In simple terms, the PCI Express lanes in a computer are much similar to the highways where vehicles travel in both directions simultaneously.
However, with respect to the computers, the vehicles represent the data transmitted to and from the processor or motherboard.
Ideally, every processor or the Central Processing Unit can support only a limited number of PCI Express lanes.
Traditionally, any consumer grade Intel CPU will support up to 16 of these lanes while, on the other hand, the AMD processors may support up to 20 PCI Express lanes.
However, server CPUs and high-end enthusiast CPUs may support more PCI Express lanes.
Higher the number of these lanes allotted to the component, the better will be the tasks performed by it due to the more profound impact.
Ideally, the bandwidth of the PCI Express e lanes may limit the optimal performance that can be offered by a component, say multiple Graphics Processing Units or GPUs for example, that may be connected to the PCI Express slot.
Ideally, in order to identify the right type and amount of PCI Express lanes for your computer, you will need to understand the configurations and generations of the PCI Express in the first place.
And, everything should be based on these configurations as well as on the workload.
About PCI Express
Peripheral Component Interconnect Express refers to the interface.
It allows connecting several high speed devices to the computer such as:
There are typical PCI Express connectors that look just like any other type of expansion slots on a motherboard allowing you to attach these devices physically to the computer.
As a general rule, each PCI Express connector comes with a varied number of lanes such as 1, 4, 8, 16, or 32 to transfer data, and, as you know, the bandwidth offered also increases in a linear fashion with the increase in the number of PCI Express lanes.
PCI Express Lanes and Workload
Ideally, most of the graphics cards that are available in the market today need 8 PCI Express lanes at least to function at their optimal performance level while being used for rendering applications or while playing games.
Even if a few graphics cards can operate with a lower number of PCI Express lanes, there will be a significant drop in the performance noticed.
That is why, especially in multiple GPU configurations, it is recommended that every GPU has at least 8 PCI Express lanes in them, unless they encounter negligible workload.
The workload on a PCI Express bus can be reduced with features such as NVLink from NVIDIA.
This feature will allow stacking the VRAM or Video Random Access Memory across several GPUs.
However, this benefit may not be available with the consumer cards since they do not support such features.
In that case, it is best to invest in a system with an adequate number of PCI Express lanes for numerous GPUs in order to reduce the workload without needing the NVLink support.
Ideally, it all depends on the manufacturer as to how many lanes will be allocated to a particular slot on a motherboard or a device.
Therefore, it may vary.
For example, it is not always true that the PCI Express x16 slots on the motherboard for a graphics card will use 16 PCIe lanes.
Ideally, the number will change depending on several different factors such as:
- The type and model of the processor
- The motherboard chipset type and
- The number of GPUs.
Moreover, when two GPUs are run on a motherboard, one slot may operate with just 8 lanes out of the available 16 physical PCI Express lanes in the above example due to the limitations of the processor.
However, there will not be any significant difference in the performance of the GPU whether it uses 8 lanes or 16 lanes if only the motherboard uses a PCIe Gen 4 and the GPU also supports PCIe 4.0.
For that matter, even a PCIe Gen 3 graphics card will offer reasonably good performance.
If only the motherboards and the generations of the GPUs are older, there will be a significant impact on the performance.
It is for this reason you should check how exactly the motherboard splits up the PCI Express Lanes available onto its different connectors.
The PCI Express lanes on the motherboard typically originate either from the motherboard chipset or from the processor itself.
However, the lanes on the processor are usually reserved for the x16 slots graphics cards exclusively.
Apart from that, it may also be reserved for the M.2 slots in order to connect the high-speed SSDs because they need to transmit data without experiencing any bottleneck by the chipset.
On the other hand, the chipset lanes can be connected to different things such as:
- The onboard USB
- Other M.2 slots
- PCIe slots and
- SATA or Serial Advanced Technology Attachment.
There is an exclusive 4-lane PCI Express bus that is used by the chipset itself to transfer data to the CPU.
Every device that is connected to the computer through the PCI Express lanes will have a cap to the maximum bandwidth.
This may cause bottlenecks at times.
When you choose a motherboard, you must check that the PCI Express slots that you want to use are connected directly to the processor.
This will ensure that there is no issue with the bandwidth that may result in bottlenecks.
You may use a PCI Express slot wired to the chipset but then that will not eliminate the chances of bottlenecks.
The best way to identify the physical PCIe x16 slot connections is to check the lanes allotted to it.
Typically, if there are 16 or 8 lanes it will be directly linked with the processor.
Usually, it is the PCI Express slot at the top that will connect to the processor but it is always prudent to check it out with the motherboard manual to be absolutely sure.
Varying PCI Express Requirements
Typically, the eventual graphics performance of a computer will depend on the type of the job and GPU you use and their number.
Based on that, there will be varied requirements of PCI Express lanes by the graphics cards for it to perform optimally.
For General Rendering Tasks:
A large amount of bandwidth is required for rendering tasks and for that even a single GPU of the current generation may perform pretty well regardless of using 8 or 16 lanes of PCIe Gen 3.0 or PCIe Gen 4.0.
When the GPU or any other PCIe supported device performs at almost the maximum bandwidth offered by the PCI Express lanes, the lanes are considered to be saturated.
The degree of saturation will vary in the connections depending on the number of PCI Express lanes available and the generation of PCIe used.
That is why it is said that for running multi-GPU setups to achieve the best performance it is best to run each GPU on 8 lanes.
Running them in 4 lanes is possible and there will be just a slight drop in the performance but it is not recommended.
The type of workloads run will also determine the level of PCIe Lane Scaling.
For example, if games are played and simple 3D scenes are rendered, it will fit easily in the Video RAM of the GPU.
For that matter, it will not need to communicate over the PCI Express bus and there will be almost no bottlenecking as well even if you are using fewer number of PCI Express lanes than what is recommended.
However, bottlenecking can be a more pronounced issue when there is a need for constant communication with the processor or accessing the memory of the computer system frequently.
Video Editing and Graphic Design Tasks:
These are quite graphics intensive tasks and therefore it is recommended that you use at least 16 dedicated lanes for the GPU.
This will help you in graphics design and video editing workloads with an added high-speed storage option.
3D Animation and Rendering Tasks:
At least 8 PCIe Gen 4 lanes are recommended for these types of tasks for every physical x16 slot on a motherboard for four GPUs.
However, if you do not want to use those many GPUs, you may populate the extra empty PCI Express slots with network cards or storage according to your requirement.
If you are a regular gamer, it will be enough for you to use just 16 PCI Express Gen 3.0 or Gen 4.0 lanes for reasonably good performance.
This is because most of the graphics cards will not be able to saturate the bandwidth easily.
However, if you want low latency, using a PCIe 4.0 in place of PCIe 3.0 is better as this will offer a slight gain in the performance while playing a game in comparison to the PCIe 3.0.
As such, gaming does not demand a large number of PCI Express lanes just as other more intensive jobs and features would such as multi-GPU Scalable Link Interface or SLI and Crossfire.
Selecting the Right Amount of PCIe Lanes
Now that you know that you need the right amount of PCI Express lanes for optimal performance, there are a few factors to look into in order to make sure that you select the right amount of these lanes.
Selecting the right processor is very crucial in order to ensure that it is capable of supporting at least 16 PCIe 3.0 or PCI e 4.0 lanes.
This will enable you to do jobs like graphics designing, video editing, and also play general games.
The next important factor to consider is to select the right types of motherboard because a suitable processor alone cannot guarantee that you will always get the desired number of PCI Express lanes.
It is only when the processor and the motherboard are both suitable the PCI Express link of the chipset and the PCI Express 4.0 support will be just as desired.
Working of PCI Express Lanes
Typically, PCI Express is a specific type of protocol that comes with multiple layers such as:
- A transaction layer
- A physical layer and
- A data link layer.
Here the data link layer is most important which is further divided into a MAC or Media Access Control layer. Each of the lanes comes with two unidirectional differential pairs. These pairs operate at different speeds based on the negotiating capacities such as:
- 2.5 GB/s
- 5 GB/s
- 8 GB/s and
- 16 GB/s.
On the other hand, there are separate differential pairs for receiving and transferring data. All of these add up to a total of 4 data wires in each lane.
Each of these lanes are able to establish an independent connection with the PCI controller or Southbridge of the processor chipset or the processor itself which is the graphics card slot in most of the cases and the expansion card.
The bandwidth scales in a linear fashion which means that the bandwidth of a four-lane connection will be double the bandwidth of a two-lane connection.
The slot may be required to be sized according to the requirement of bandwidth by the expansion card.
Ideally, in a physical PCI Express x16 slot you can put up an x1, x4, x8, or x16 card and you can also run an x16 card at x16, x8, x4, or x1.
On the other hand, a PCI Express x8 slot can support an x1 or x4 or x8 card. However, it cannot support an x16 card.
Just to make matters more confusing, there are different versions of the PCI Express interface just as a motherboard can come with multiple sizes of slots on it.
The different PCI Express versions are:
- PCIe 1.0a
- PCIe 1.1
- PCIe 2.0
- PCIe 2.1
- PCIe 3.0
- PCIe 3.1
- PCIe 4.0 and
- PCIe 5.0.
Through the PCI Express lanes the data is sent in single bits and larger the number of lanes, the more data can be sent.
However, the lane may not be occupied always or fully saturated when occupied and the devices connected to the lanes may not always use its full capacity.
Compatibility of the PCI Express lanes is an important thing to know in this matter.
The cross compatibility of the PCI Express lanes allow plugging in a PCIe x1 device in a PCIe x16 slot.
The device will not malfunction due to the cross compatibility of the PCI Express standard.
This means that you can plug in a small expansion card in a slot that has more lanes than it is required by the device.
Though the device will work, the larger slot may not offer any gain in the performance of it.
However, putting a smaller expansion card into a larger slot is not recommended because it will waste the potential of the slot which could have been used fully by a full-size and more demanding expansion card.
It is for this reason most of the motherboards come with a number of slots, both of large and small size, as well as number of lanes.
The number of slots will however depend on the number of PCI Express lanes as well as on the form factor of the motherboard.
However, looking at it from the other way around, if you plug in a larger PCIe x16 graphics card into a smaller x8 PCI Express slot, it will theoretically halve the overall bandwidth.
However, it may not necessarily mean that the level of performance will also be halved as compared to when it is used in an appropriate slot.
It all depends on the transfer rate that is needed and is ideal for the graphics card. If it is not suitable, it will not offer any benefits.
The backward compatibility of the PCI Express devices and the slots plays a significant role here by allowing such type of irregular usage.
This means that there will not be much of an issue if you use a PCI Express 3.0 expansion card on a PCIe 2.0 slot.
This is because the entire setup will then run at the speed of the PCIe 2.0 slot.
The working will depend on the bandwidth but the PCI Express lanes are not the only driver of it.
The PCIe version is also very important for it.
Typically, the newer versions of PCI Express will have double the bandwidth and speed of the processors.
The number of lanes a Graphics Processing Unit will use will depend on the workload and the number of lanes used by the Central Processing Unit will depend on the version of PCI Express used.
Sixteen lanes are good enough for a single GPU but for any regular consumer workload, an x8 slot will be sufficient in general even if you run any graphics intensive apps or games.
In comparison, a higher number of lanes in a CPU is recommended with a multi-GPU configuration since that will not saturate the PCI Express lanes.
For graphics intensive apps and modern games a PCIe 4.0 is recommended but for simple data transfer a PCIe 3.0 is absolutely fine.
However, anything lower than that may not be sufficient to handle the growing demands of graphics rendering.
What are the Uses of PCI Express Lanes?
The PCI Express lanes are typically used in a couple of places inside the computer such as:
The CPU will have a number of these lanes, in fact 16 of them, connected to it and to at least one of the x16 slots on the motherboard.
There are also a few found for video cards. It can be a single card using the entire channel or several cards using a portion of the channel each.
How the lanes will be used will depend on the number of video cards used.
If there are two slots for motherboards and two cards are used, each of them may use 8 lanes.
On the other hand, if there are three cards used, one may use 8 lanes and each of the other two video cards may use 4 lanes.
Some specific models of CPUs may have a larger number of video card lanes such as up to 40 as you would find in those Intel X series chips.
Some of these lanes may connect the CPU to the PCH or the Platform Controller Hub.
These lanes are called the Direct Media Interface or DMI lanes by Intel but are the same as the PCI Express lanes.
From the PCH, these lanes go to different places such as:
- To the SATA controller
- To the NVMe-compatible M.2 slot
- To the USB controllers and also
- To the PCIe slots on the motherboard.
The PCH functions as the multiplexer and eventually all of the devices connected will share the DMI lanes available while communicating with the processor or the main memory of the system via Direct Memory Access or DMA.
The PCI Express lanes are used to control different functions such as:
- Onboard video
- PCIe 3.0 x16 slot used typically for video card
- 2/U.2 and LAN or Local Area Network on a few Enthusiast Boards.
The PCI Express lanes of the chipset may also be used to control some other functions such as:
- Onboard sound and RAID or Redundant Array Of Independent Disks
- SATA hard drives
- Onboard Network Controller or LAN
- PCIe slots and
Ideally, the PCI Express lanes do not affect the performance of the CPU. It simply is the means to connect the different components within the computer.
How Many PCIe Lanes are Needed?
The number of PCI Express lanes you will need will largely depend on the type of expansion cards you want to use as well as the number of them you want to use.
However, all of the lanes the processor or the motherboard offers may not be usable or connect to the PCI Express slot to install an expansion card.
Different components of the computer will need different bandwidths and therefore will have varied lane requirements such as:
- Each x16 PCIe video cards will need 8 to 16 lanes
- All other specialized PCI Express cards will also need 8 to 16 lanes
- The M.2 drives will need 4 lanes
- Thunderbolt will use 4 lanes PCIe 3.0
- Any hardware based RAID controller will need 4 lanes
- SSD drives will need 2 lanes each
- USB 3.1 Gen 2 drives will need 2 lanes
- USB 3.0 or USB 3.1 Gen 1 drives will need a single lane and
- Sound cards and network controllers will need one lane as well.
It is only when the component gets the desired number of lanes to function it will produce the optimal results.
So, it is important to ensure that the total number of PCI Express lanes is just enough to deal with the total PCI Express requirements of the devices that you wish to add to your computer system.
Therefore, the answer to this question may not be specific since it will vary according to the component and the PC architecture.
Here is a brief list of components and their respective lane requirements:
- For NVIDIA or AMD Graphics, 16 lanes are required
- For PCIe storage in Intel 905p, Samsung 970 Pro, and others, 4 lanes are required
- For RAID cards, 4 to 8 cards are required
- For USB cards and 802.11 Wi-Fi, only one lane is enough.
The number of PCI Express lanes you will need will also depend on the specific type of processor and the chipset as well.
Each different model will come with a varying number of PCI Express lanes in them.
For example, most of the Intel Core i5 and i7 processors will come with 16 lanes in them but there are a few specific models of Intel Core i9 processors especially belonging to the 9000x-series that may come with as many as 44 lanes in them.
As for the number of lanes offered by the chipset, it will mainly depend on the architecture of the motherboard.
Usually it ranges between 4 and 24. The chipset lanes are normally used for:
However, the lanes of the chipset can be shared between the components but for that the total number of lanes must be limited.
This means that if the M.2 slots share the lanes with the SATA ports, both cannot use the lanes simultaneously.
One will have to be inoperable when the other uses the PCI Express lanes.
It is due to this limitation that the chipset lanes are usually not able to handle the high demand for bandwidth by the GPUs.
Therefore, sometimes, the chipsets may be overloaded and cause bottlenecks.
In order to offload them, the CPUs usually have their dedicated PCI Express lanes connected to the PCIe expansion slots directly.
These PCI Express lanes on the CPU are normally connected to the primary and secondary expansion slots.
These slots are typically located closer to the CPU.
The primary slot is normally a PCIe x16 expansion slot but, in comparison, the secondary slot is typically an x8 slot.
However, this can vary depending on the design of the manufacturer.
Both these two slots are occupied by the GPU due to its high demand for bandwidth.
The CPUs also provide lanes to the other components to link with them depending on their design.
For example, the PCI express lanes of the Intel processors are connected directly to the PCIe x16 expansion slot.
However, these CPU lanes are not shared between the devices and therefore optimal performance from the CPU and the devices connected to it can be expected.
Among all of the PCI Express lanes available, the top PCIe x16 slot is reserved for the GPU.
This is because this slot has the highest number of lanes and thus can offer higher bandwidth which is usually the primary requirement of the GPUs.
The GPUs usually need to operate at a high transmission rate than the other expansion cards because they have to deal with a huge amount of graphical data that are used for different applications such as:
- Machine learning
- Artificial Intelligence
- Cinematic applications
- 3D rendering and more.
You may still get something to be satisfied about by using a PCIe x8 or a PCIe x4 slot, but it will hardly meet the bandwidth requirement of the GPUs due to fewer lanes in them.
Therefore, you can expect to have a significant drop in the level of performance.
How to Check the Number of PCIe Lanes?
You can check the number of PCI Express lanes your GPU is using in a couple of ways. These ways are quite easy and do not need any technical expertise.
- One, you can physically inspect it, if you know exactly how to go about it, especially in a desktop computer and
- Two, you can use any third party software, especially in a laptop computer.
When you physically inspect it, check the slot on the motherboard to which the graphics card is inserted into.
If it is using the top or the first PCIe slot of the motherboard, then it is surely using 16 PCI Express lanes.
However, if the motherboard comes with three PCIe x16 slots and if the graphics card is installed into the second or the third one, it is using 8 lanes and 4 lanes respectively.
This is easy because this is the particular way in which the PCI Express x16 slots are hardwired on a commercial motherboard.
Alternatively, if you are using any free third-party software such as GPU-Z to check the number of lanes being used by the graphics card of your computer, you will have to install and run the application and look for the Bus Interface field.
The number of PCI Express lanes your GPU is using will be displayed there, along with the version of it.
As for the others, here are the numbers:
- An NVMe SSD inserted into an M.2 slot will be using 20 PCI Express lanes but in others it will use 4 PCIe lanes
- A Wi-Fi card in an x1 slot will be using 21 PCI Express lanes and
- A 4K video card in one of the x16 slots will be using a total of 25 PCI Express lanes.
Sadly, you do not have any specific automatic calculator for determining the PCI Express lanes. You will have to do it all yourself by simply looking at the motherboard and CPU physically or their spec sheet.
It is hard but is very important to determine the number of PCI Express lanes the CPU or the chipset support if you are building your own PC.
This will help you to know whether or not the interface will be saturated and to future proof your system. This article has surely helped you to know all that.