What is PCI Express? Do PCIe lanes, slots, and versions matter?

PCI Express is one of the most important technologies for modern computing, powering the connections between motherboards and high-performance peripherals like graphics cards, solid-state drives, and network adapters. In this article, I try to shed some light on what PCIe lanes are, what types of PCIe slots are there, and what to expect from each PCIe version. So, if you want to know more about all that, read on:

What is PCI Express and what does it stand for?

PCI Express stands for Peripheral Component Interconnect Express and represents a high-speed interface standard used to connect various hardware components to a motherboard. In other words, PCI Express (or PCIe abbreviated) is an interface that connects internal expansion cards such as graphics cards, storage devices, Ethernet and Wi-Fi adapters to the motherboard. Over time, PCIe has evolved to deliver exponentially faster data transfers. PCIe is now also fundamental for NVMe solid-state drives (SSDs).

PCIe expansion and M.2 slots on a modern motherboard

What types of PCI Express slots and sizes are there? What do PCIe lanes mean?

PCI Express uses physical slots to interconnect the expansion cards to the motherboard. The common PCI Express slots we see on motherboards are PCIe x1, PCIe x4, PCIe x8, and PCIe x16. The number that comes after the “x” letter tells you the physical dimensions of the PCI Express slot and is determined by the number of pins on the slot. The higher the number, the longer the PCIe slot, and the more pins that interconnect the expansion card to the slot.

Furthermore, the “x” number also tells you how many lanes are available in that expansion slot. Here’s how the commonly used PCIe slots compare:

• PCIe x1: Smallest slot, 1 lane, 18 pins, and 25 mm in length
• PCIe x4: Moderate size, 4 lanes, 32 pins, and 39 mm in length
• PCIe x8: Larger slot, 8 lanes, 49 pins, and 56 mm in length
• PCIe x16: Largest slot, has 16 lanes (ideal for GPUs), 82 pins, and 89 mm in length

PCI Express slots, lanes, pins, and physical dimensions

PCI Express lanes are paths between the motherboard chipset and PCIe slots or other devices that are part of the motherboard, such as the processor socket, M.2 SSD slots, network adapters, SATA controllers, or USB controllers.

PCI Express x16 slots

In PCI Express, each lane is individual, meaning that it cannot be shared between different devices. For example, if your graphics card is connected to a PCIe x16 slot, it means that it has 16 independent lanes dedicated just to it. No other component can use those lanes except the graphics card.

Here’s an idea that might make it easier for you to grasp what PCI Express lanes are: just imagine that PCI Express is a highway, and the cars that drive on it are the data that’s being transferred. The more lanes you have available on a highway, the more cars can drive on it; the more PCIe lanes you have, the more data can be transferred.

PCI Express is like a highway, and PCIe lanes are its… lanes

A PCI Express card can fit and work on any PCIe slot available on the motherboard, as long as that slot isn’t smaller than the expansion card. For example, you can fit a PCIe x1 card in a PCIe x16 slot. However, you can’t do the opposite. You can mount, for instance, a PCIe x1 sound card in a PCIe x16 slot, but you cannot mount a PCIe x16 graphics card in a PCIe x1 slot.

A PCIe x1 card in a PCIe x16 slot

NOTE: I’ve heard someone use a strange term: PCIe port. No, there isn’t technically a component called a PCIe port! What they were referring to was likely a PCIe slot.

What PCIe versions are there? What data transfer speeds (bandwidth) do they support?

Since its introduction, each new PCIe version has doubled the bandwidth of the previous one. Here’s a quick breakdown of their lane speeds:

• PCIe 1.0 (introduced in 2003): 250 MB/s per lane
• PCIe 2.0 (introduced in 2007): 500 MB/s per lane
• PCIe 3.0 (introduced in 2010): 984.6 MB/s per lane
• PCIe 4.0 (introduced in 2017): 1.969 GB/s per lane
• PCIe 5.0 (introduced in 2019): 3.938 GB/s per lane
• PCIe 6.0 (introduced in 2022): 7.56 GB/s per lane
• PCIe 7.0 (likely to be introduced in 2025): 15.13 GB/s per lane

The most recent version, PCIe 6.0, introduced in 2022, delivers a remarkable 7.563 GB/s per lane. However, its adoption is currently limited to data centers and high-performance computing environments, primarily for enterprise and server use.

Moreover, I also included PCIe 7.0. That’s because PCIe 7.0 is already in development. However, the specification is not yet ready, but will probably be finalized in 2025. Just don’t expect to see it in consumer-grade hardware anytime soon.🙂

Remember that PCIe slots can offer not just one, but more lanes? The bandwidth values we shared are multiplied by the number of lanes available on a PCIe slot. If you want to calculate how much bandwidth is available for a certain expansion card, you have to multiply its PCIe bandwidth per lane with the number of lanes that are available for it.

For example, a graphics card that supports PCI Express 5.0 and is connected to a PCIe x16 slot has access to a total bandwidth of about 63.02 GB/s. That’s the result of multiplying 3.94 GB/s by 16 (PCIe bandwidth per lane * 16 lanes). Impressive, right?

Here’s how PCI Express versions scale when you take into account PCI Express lanes:

PCI Express versions and bandwidths

Is PCI Express 5.0 widely available?

For now, PCI Express 5.0 is the fastest specification available for home computers. However, PCIe 5.0 is available only in some consumer motherboards:

• AMD AM5 platforms (Ryzen 7000 and 9000 series) support PCIe 5.0 for GPUs and NVMe storage.
• Intel’s 12th Gen and newer CPUs (Alder Lake, Raptor Lake) also support PCIe 5.0.

High-performance PCIe 5.0 NVMe SSDs are becoming increasingly available, delivering impressive sequential read and write speeds exceeding 12 GB/s. However, their adoption remains limited, primarily appealing to enthusiasts and professionals who demand top-tier performance for tasks like high-resolution video editing, data-intensive applications, and gaming. For most consumers, PCIe 3.0 and 4.0 SSDs are still the go-to options, offering excellent performance for everyday use at a much lower cost.

A PCIe Gen5 x4 NVMe M.2 SSD

On the other hand, all the current graphics cards for consumers work on PCIe 4.0 or older. Looking ahead though, rumor has it that NVIDIA’s upcoming RTX 50-series GPUs, expected to launch in 2025, may come with PCIe 5.0 interfaces.

How does PCI Express affect the speed of your graphics card?

Some people are asking an interesting question: Does the faster and newer PCI Express 4.0 specification positively affect the speed of the graphics card? The quick answer is no, it doesn’t, and you do not get more frames per second! Here’s why:

When you are playing a game, the graphics card uses its dedicated RAM (GDDR) to hold the textures used for rendering the frames on the screen. Besides the GPU clocks, that graphics memory is the most important thing for how many frames you get each second.

The graphics card only has to use the PCI Express interface that connects it to the motherboard when it needs to communicate with the processor or load textures from the system memory (the computer’s RAM). That’s not supposed to happen often, as modern graphics cards have a lot of dedicated RAM of their own. And even if/when it happens, once the textures have been transferred via the PCI Express interface from the system RAM and have been loaded into the graphics card’s memory, they stay there. The reason for that is that the graphics memory is a lot faster than the system’s RAM.

GIGABYTE GeForce RTX 4080 SUPER WINDFORCE 16G: a graphics card that supports PCI Express 4.0

None of the graphics cards available today need the full bandwidth offered by the PCI Express 4.0 x16 slots. Not to mention PCIe 5.0! Check this article from TechPowerUp to see why I say that: NVIDIA GeForce RTX 4090 PCI-Express Scaling.

What about PCI Express versions compatibility?

All PCI Express versions are compatible with one another. For example, a PCI Express 4.0 graphics card works even if you connect it to a motherboard that only supports PCI Express 3.0 or even 2.0. However, the bandwidth of the PCI Express interface is limited by the smallest factor. For example, if you connect a PCI Express 5.0 graphics card or a SSD to a motherboard that only supports PCI Express 4.0, that GPU or SSD works on PCIe 4.0. Instead of having access to a bandwidth of 15.75 GB/s, it can only use 7.88 GB/s, so its maximum theoretical speed is halved.

Do you have any other questions regarding PCI Express?

Now, you should have a better idea of what PCI Express is all about. You should also understand more about the different types of PCIe slots, lanes, and versions, so you can impress your friends or, at the very least, your pet.🙂 Do you have any other questions that I might help you get an answer to? If you do or if you have something to add to this article, please leave a comment below.