What Is PCIe 4.0, and Why Does It Matter?

PCIe 4.0 devices are becoming increasingly prevalent. Support for PCIe 4.0 is a key feature of 11th Gen Intel Core CPUs and motherboards, which provide up to 20 CPU PCIe lanes.

But what is PCIe 4.0, and what makes it different from PCIe 3.0? What are the benefits of CPU PCIe lanes over chipset PCIe lanes?

Let’s dive in to explore how PCIe 4.0 works and why it’s an integral part of the 11th Gen platform.

What Is PCIe 4.0?

If you’ve built a PC before, you’ll recognize the PCIe slots running horizontally across your motherboard. PCIe (Peripheral Component Interconnect Express) is a high-bandwidth expansion bus commonly used to connect graphics cards and SSDs, as well as peripherals like capture cards and wireless cards.

On the motherboard, PCIe lanes appear in x1, x2, x4, x8, and x16 variations. More lanes mean more bandwidth, as well as a longer slot. GPUs are usually installed in the top x16 slot, as it has the most bandwidth and, traditionally, the most direct connection to the CPU. Modern PCIe m.2 SSDs use x4 lanes.

Why is PCIe 4.0 replacing 3.0? Because it’s designed to be twice as fast. While PCIe 3.0 had a data transfer rate of 8 giga transfers per second, PCIe 4.0 transfers data at 16 GT/s. (The bit rate is measured in giga transfers to show the theoretical max speed before encoding—realized speeds may be slower.)

On the surface, PCIe 4.0 slots look the same as 3.0. They also feature both backward- and forward-compatibility: not only can you connect a PCIe 3.0 SSD to a PCIe 4.0 slot, you could also connect a PCIe 4.0 SSD into a 3.0 slot.

How Does 11th Gen Support PCIe 4.0?

A key advantage of 11th Gen Intel Core CPUs like the Intel Core i9-11900K and Intel Core i7-11700K is that they both provide up to 20 CPU PCIe 4.0 lanes.

This makes 11th Gen systems significantly more flexible than those from previous generations that provided only 16 CPU PCIe lanes.

Not all PCIe lanes work the same way — CPU PCIe lanes connect directly with the CPU, whereas chipset lanes (or “PCH lanes”) go through the motherboard’s chipset, which connects to the CPU via a DMI (Direct Media Interface) link.

The PCH usually manages features on your motherboard such as USB devices, Wi-Fi and Ethernet networking, and onboard sound. Because the link between the CPU and chipset is limited to x8 3.0 total bandwidth, it’s possible to saturate the link if you plug in multiple storage devices and use other resources.

Connecting directly to the CPU bypasses this bottleneck. That’s why the four extra CPU PCIe lanes provided by 11th Gen Intel Core CPUs are so valuable.

This means PC builders finally have the flexibility to give a GPU and an NVMe SSD the optimal path to their CPU at the same time. (With 16 lanes, this was only possible by halving the bandwidth to the GPU, creating a potential bottleneck.)

PCIe m.2 SSDs and NVMe SSDs using riser cards already enjoy speed advantages over drives that connect over a SATA data cable. The higher throughput of PCIe allows NVMe storage to rapidly queue more data, and direct connection to the motherboard reduces latency. Connecting to CPU PCIe lanes further reduces latency by eliminating the distance data must travel through the chipset.

Why Upgrade to PCIe 4.0?

As mentioned above, PCIe 4.0 is designed to double the throughput of 3.0. But the real benefit of PCIe 4.0 compatibility is the option to upgrade to new SSDs and GPUs as the technology matures.

New PCIe 4.0 SSDs are designed to have higher maximum read/write speeds than PCIe 3.0 SSDs, but their current real-world advantages in areas like loading times and large file transfer are small. Over time, however, new memory controllers will be released and both games and applications are expected to take greater advantage of modern SSDs.

One way this may happen is through upcoming technologies like DirectStorage, which are designed to improve SSD performance in heavy I/O workloads. As SSDs become the norm in next-gen game development, this could lead to advances in load times, asset streaming, and level design.

The expected higher bandwidth of PCIe 4.0 may also benefit graphics cards, as higher throughput helps allow quicker transfer of data to VRAM. But while PCIe 4.0 setups outperform 3.0 in synthetic benchmarks, the real-world benefits for gaming are currently minor.

Some tests suggest that even running games in 4K with current graphics cards won’t saturate the bandwidth of a PCIe 3.0 x16 slot. There may be minor FPS advantages when comparing the same GPU running in PCIe 4.0 configuration against 3.0, but the differences are small enough to be unnoticeable.

In short, 11th Gen desktops provide a platform that gives you the freedom to upgrade. They ensure you can get the most out of future devices that will further unlock the potential of PCIe 4.0.

What Do I Need for PCIe 4.0?

CPU. First, you’ll need an 11th Gen Intel Core desktop CPU, which are built to support gaming from the ground up with features like PCIe 4.0 and up to 20 CPU PCIe lanes.

Motherboard. You’ll also want a motherboard from the Z590 or B560 lines, which provide up to 20 CPU PCIe 4.0 lanes.

Z590 boards have additional performance advantages, such as a x8 DMI link that helps prevent bottlenecks in communication between the chipset and CPU. (As with PCIe, more DMI lanes means enhanced speeds; before 11th Gen, motherboards used x4 DMI links.)

PCIe 4.0 devices. Though you might not spring for a PCIe 4.0 SSD or GPU during your initial build or purchase, it’s easy to see why support is useful down the road. Maybe ports of new console games start relying more heavily on streaming in assets, and a PCIe 4.0 SSD provides a tangibly smoother experience. Or the next generation of GPUs benefits from the doubled throughput of PCIe 4.0 slots. (Note that PCIe 3.0 devices will also work normally on a PCIe 4.0 platform, thanks to backwards compatibility.)

Why Does PCIe 4.0 Matter?

A PCIe 4.0 platform gives you more flexibility. You’ll have more choices when you shop for new peripherals and more choices when you configure them.

Many users replace either their storage drive or graphics card at some point in the lifetime of their system. If you’re one of them, PCIe 4.0 support ensures that you’ll be able to use cutting-edge SSDs and GPUs released in the next few years to their full capability. (PCIe 4.0 devices will still work in PCIe 3.0 platforms, but performance may suffer due to decreased bandwidth.)

Additionally, 20 CPU PCIe lanes give a system’s two most important peripherals — the GPU and SSD — a more direct connection to the CPU, potentially reducing latency.

It’s difficult to predict what new peripherals anyone might want a year or two down the line, but 11th Gen systems are designed to get the optimal performance from them.