What is PCIe 4.0 & Should You Upgrade Your System in 2024?

PCIe 4.0 is the fourth generation of the Peripheral Component Interconnect Express (PCIe) standard. This high-speed serial expansion bus standard is found in almost every modern-day computer. PCIe powers fast connections between different components, such as the GPU, CPU, and NVMe-based SSDs.

While slowly being replaced by its successor, PCIe 4.0 slots are found in almost every motherboard built in the last few years. As the demand for high-speed computing increases, we need faster, more reliable, and scalable data bus connections. So let’s discuss more about the PCIe standard itself;

The PCIe Standard

PCIe adopts serial full-duplex communication, wherein data can be sent and received simultaneously between the sender and receiver. On the software side, PCIe is backward compatible with the old PCI standard, even if support is not available. Likewise, PCIe is backward compatible with itself, that is, you can use a PCIe Gen 4.0 SSD in a PCIe 3.0 slot.

Between any two devices, PCIe supports links between 1 – 16 lanes. An x1 slot transfers data at the rate of 1 bit per second, an x4 slot transfers data at 4 bits per second, and so on.

During the initialization phase, the number of lanes used can be reduced to the maximum amount supported by both devices. It is possible to place an x1 PCIe device in an x16 slot, but the bandwidth will be limited. Similarly, using an x16 PCIe card in an x8 slot is also possible. Generally, links having the following widths have been specified;

• PCIe x1
• PCIe x4
• PCIe x8
• PCIe x16

This allows not only high-bandwidth devices (GPUs) but also lightweight networking devices such as Gigabit Ethernet to be supported by the standard. Within your motherboard, the vertical bars that you often see are PCIe slots. Any device placed atop these slots is connected with the CPU directly or is routed via the PCH to the CPU.

READ MORE: NVMe PCIe M.2 Vs. SATA – Which Should You Buy and Why? ➜

Advantages of PCIe

Being the official standard in every PC, PCIe has a lot of tricks up its sleeve. It is highly scalable, fast, hot plug capable, backward compatible, and future–proof. Let’s discuss these advantages one by one;

1) High Bandwidth

PCIe provides significantly higher speeds as compared to older standards. This is accomplished through its multi-lane system to increase data transfer rates. Moreover, each iteration of PCIe doubles the speed of the last generation. PCIe 4.0 can push 16 GT/s (Giga Transfers) per lane, or almost 32 GB/s across an x16 link.

A table from Wikipedia shows the bandwidth, data transfer rates, and technology behind all PCIe versions;

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2) Scalability

Motherboard vendors can configure PCIe slots in almost any slot size, provided it conforms to the standard. GPUs are typically slotted in the 1×16 slot, whereas NVMe SSDs have designated x4 slots for them.

The PCH on your motherboard often uses an x4/x8 link to communicate with the CPU. This link allows various devices such as ethernet controllers, WiFi cards, and additional NVMe SSDs to communicate on a single x4/x8 slot. We’ll discuss more about CPU and PCH lanes in a later section.

3) Future Proofing

PCIe has various future revisions planned out, including PCIe 6.0 and PCIe 7.0. The latest edition is PCIe 5.0, which packs 32 GT/s per lane or nearly 64 GB/s across 16 lanes. Intel’s 12th Generation (Alder Lake) CPUs were the first x86 CPUs to incorporate PCIe 5.0 support.

AMD’s Zen4 followed with upwards of 24 PCIe 5.0 lanes. In the GPU market, NVIDIA’s current GH100 GPU provides support for PCIe 5.0. The Chinese GPU, Moore Thread’s MTT S80, is technically the first consumer GPU with PCIe 5.0 support, however, support and availability are extremely limited.

PCIe 6.0 and 7.0 plan to increase bandwidth to 64 GT/s and 128 GT/s respectively. In a 16-lane layout, this yields 128 GB/s and 242 GB/s of bandwidth respectively. Currently, the NVIDIA Blackwell-based GB100 is the world’s first PCIe 6.0 GPU.

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CPU vs PCH PCIe Lanes

What if we tell you that not all PCIe lanes are the same? A typical Z790 has 16 PCIe 5.0 and 4 PCIe 4.0 lanes, directly linked with the CPU. Let’s establish a few basics first. Data flows from your GPU/SSD/Networking devices to the CPU, this is accomplished through the PCIe standard.

↪ The Distinction

Staying on topic, alongside the direct lanes, there exist other lanes for low-bandwidth devices, such as WiFi, networking, and onboard sound. To accommodate for these devices, the chipset or PCH on your motherboard has additional downstream lanes. So data flows from your ethernet to the chipset (PCH), which sends this data to the CPU.

In the diagram above, the chipset has 20 PCIe 4.0 lanes and 8 PCIe 3.0 lanes (left side) which seem like a lot but they are connected using a narrow x8 DMI 4.0 (16 GB/s) link to the CPU. Any sort of data that flows through these lanes faces latency and can easily saturate the rather narrow link.

You may also hear of the term “HSIO lanes“, which are High-Speed Input-Output lanes used to connect all the PCIe lanes on your system. They are of not much concern to the average consumer. For context, the Z790 chipset offers 38 high-speed I/O lanes, divided into 20 PCIe 4.0 and 8 PCIe 3.0 lanes and others reserved for connectivity.

↪ Real World Impact

On the same Z790 motherboard, you can use the top slot (x16 PCIe 5.0) for the GPU, and the bottom slot (x4 PCIe 4.0) for a fast NVMe drive (Up to 8GB/s). Any other NVMe SSD will be routed from the PCH, or through the x8 DMI 4.0 (equivalent to x8 PCIe 4.0). If you connect several SSDs and other storage media, you can easily exceed the limits of the DMI link (16 GB/s).

Moreover, on the mid-ranged B660, the link is constricted to just x4 DMI 4.0 (8 GB/s). In the case of AMD’s X670E, the CPU natively features 24 PCIe 5.0 lanes and 4 General Purpose PCIe 4.0 lanes. The chipset offers 12 extra PCIe 4.0 and 8 PCIe 3.0 lanes. However, again, the PCH and CPU are connected with a lacking x4 PCIe 4.0 (8 GB/s) link.

If you’re likely to use more than 2 NVMe SSDs, try considering a HEDT / Workstation platform. AMD’s Threadripper 7000 PRO features 128 PCIe Gen 5.0 lanes directly connected to the CPU.

READ MORE: The 5 Best PCIe Gen 4 SSDs – Best Performing M.2 Options ➜

What is PCIe 4.0?

In late 2011, PCI-SIG introduced initial specifications for the PCIe 4.0 standard, said to offer 16 GT/s or 32 GB/s in a 16-lane setup. The official launch took almost 6 years and in June 2017, PCI-SIG formally detailed the final specifications of PCIe 4.0.

AMD was the first consumer chip maker to launch CPUs with support for PCIe 4.0, starting with Zen2 and the X570E flagship chipset in 2019. Intel was a bit late to the party and PCIe 4.0 came in the blue flavor with Tiger Lake the next year.

PCIe 4.0 adopts a 128b/130b encoding technique to transform 128-bit data into 130-bits. This translates to almost 98.46% efficiency, which is much more efficient than previous iterations.

↪ Impact on SSDs and GPUs

In terms of real-world performance, a 4 lane PCIe 4.0 link for SSDs maxes out at roughly 8 GB/s. This is in line with what most consumer high-end PCIe 4.0 SSDs provide, such as the Samsung 990 PRO and WD Black SN850X.

Most GPUs feature an x8 or x16 bus interface, which is ample even for older PCIe versions. However, an outlier is the Radeon RX 6500 XT, featuring a limited x4 interface. If your PC uses PCIe 3.0 for the first x16 slot, your bandwidth will be limited to just 4 GB/s with the RX 6500 XT. This results in a performance delta of almost 70% in certain titles between PCIe 4.0 and PCIe 3.0.

Apart from that, you could miss out on a few frames with an x8/x16 card. Unless you built your PC a while back, you are most likely to have PCIe 4.0 as it was introduced with Rocket Lake-S (11th Gen) for Intel and Zen2 (Ryzen 3000) for AMD, though you’ll need a B550 or X570 at minimum.

READ MORE: RTX 3070 vs RX 6700 XT: Which GPU Should You Buy in 2024? ➜

Fear, Uncertainty and Doubt

It only took a few years for the market to see a sudden shift from PCIe 4.0 to PCIe 5.0 equipped systems. CPU manufacturers are slowly introducing more PCIe 5.0 slots with newer chipsets. Moreover, SSDs faster than 8 GB/s are technologically limited by the PCIe 4.0 standard. So, is it time to upgrade?

Generally speaking, all modern GPUs support no higher than PCIe Gen 4.0. You’d think that PCIe 4.0 and PCIe 3.0 would have a huge performance gap, but that’s not the case.

Gamer’s Nexus conducted some testing and despite the 2x bandwidth difference, the FPS marginally improved by only 2-3% between Gen 3 and Gen 4. It goes without saying that PCIe Gen 5.0 will be an even smaller improvement.

Likewise, in the SSD department, the first argument is that PCIe 5.0 supported SSDs are costly. At equivalent capacities, Gen 5 SSDs are almost 2x more expensive than Gen 4 SSDs. Secondly, the speed improvement is marginal, as PCIe 5.0 technology hasn’t reached its true potential, yet. You’d be paying 2x more for 1.5-1.6x more speeds (Upwards of 12000 MB/s).

Lastly, PCIe 5.0 SSDs run extremely hot. You almost always require a heatsink or even active cooling at times for sustained peak performance. Unless your workload can actually utilize this level of bandwidth, it is not worth the investment.

↪ Potential Benefit of Upgrading

However, a strong point in favor of PCIe 5.0 is that a few of Intel’s upcoming Z890 boards are rumored to feature an x8 PCIe 5.0 slot (equal to x16 PCIe 4.0 for 32 GB/s) for the GPU. This leaves behind 3 x4 PCIe 5.0 slots for SSDs, directly to the CPU along with another x4 PCIe 4.0 slot. So, you get the best of both worlds while supplying more than enough bandwidth to the GPU.

Do note that this is just a rumor and not all of the high-end Z890 motherboards will support this configuration.

READ MORE: Advanced SSD Buying Guide – NAND types, DRAM Cache, HMB Explained ➜

Conclusion

The takeaway is that any modern system should be equipped with at least one x16 PCIe 4.0 slot, with the additional x4 based on either PCIe 4.0 or PCIe 3.0, depending on your board model. In light of these facts, it can be easily said that you must upgrade your system based on the CPU, GPU, and other components, not the PCIe generation.

Older GPUs on PCIe 3.0 PCs may not see a huge bump in performance even if upgraded to PCIe 4.0. The same can also be said for GPUs nowadays, though funnily enough, no GPU supports PCIe 5.0 yet. If you’re on a budget, then PCIe 4.0/3.0 will do you just fine.

However, if you want a high-end system, upcoming chipsets can quite effectively give you many storage options (3 x4 PCIe 5.0 + 1 x4 PCIe 4.0), with ample bandwidth for the GPU, though you’ll need a PCIe 5.0 (x8) GPU, which as of now, do not exist. This is because the RTX 4090 will run at PCIe 4.0 x8 (16 GB/s, equal to PCIe 3.0 x16) speeds since it only supports PCIe 4.0.