PCIe 4.0 (Ultimate Guide to Understanding PCI Express Gen 4)


If you were wondering what PCIe Gen 4 is, as well as where you can find industrial grade computers that come equipped with PCIe 4.0, you've come to the right place. We will explain what PCI Express Gen 4 is in much detail below.

What is PCIe 4.0? 

PCIe 4.0 is the 4th Generation of the Peripheral Component Interconnect Express (PCIe), which is an interface standard that connects high-end components to your PC. The first generation of PCIe dates back to 2003, which was PCIe Gen 1. Over time, there have been four new versions of PCI Express. Today's focus will be the PCI Express 4th Generation because it's the latest PCIe generation to hit the market. 

PCIe doubles the data transfer speed of the previous generation (PCIe 3.0) from 1GB/s per lane to 2GB/s per lane, providing users with a total of 32GB/s in a 16 lane configuration. Furthermore, PCIe provides up to 16GT/s per lane when compared to the previous generation's 8GT/s. Each new generation of PCIe doubles the data transfer rate and total bandwidth per lane of the prior generation, paving the way for new, faster PCIe devices. 


(Photo credit: Microsemi)

Every PCincluding commercial and industrial computing solutions, comes equipped with at least one PCIe slot, with some computers having multiple PCI Express slotsPCIe slots are typically used to add GPUs, Solid-state drives (SSD) add on cards, Wi-Fi cards, and Raid Cards. 

PCIe 4.0 expansion slots on a typical PC motherboard come in four different types: PCIe x1, PCIe x2, PCIe x4, PCIe x8, and PCIe x16. These numbers signify how many lanes each PCIe slot has. The more lanes that a PCIe slot has, the more data that can be transferred to/from the add on card.  


(Photo credit: HowToGeek)

Each PCIe Lane is made from two pairs of wires, one for sending data and one for receiving data. The bandwidth scales linearly with PCIeso an 8-lane connection will have twice the bandwidth of a 4 lane configuration.  

The great thing about PCI express is that it maintains both forward and backward compatibility, supporting new and legacy technologies. PCIe is backward compatible with PCIe Gen 1, PCIe Gen 2, and PCIe Gen 3. PCIe Gen 4 will be compatible with PCIe Gen 5. However, a PCIe Gen 4 device will be limited to the 4th generation specifications when inserted into a Gen 5 slot.  

Said differently, PCIe 4.0 cards will work on motherboards with PCIe 3.0 slots, and PCIe 3.0 cards will work on motherboards with PCIe 4.0 slots. That said, although PCIe 4 cards will work on PCIe 3.0 motherboards, their speed will be limited according to PCIe 3.0 standard. 

The benefits of PCIe 4.0 will be most realized in data centers, which can utilize the new performance offered by PCIe 4.  This is so because NVMe storage technologies are saturating the existing PCIe 3.0 standard; PCIe 4 will allow them to achieve optimal performance and higher data transfer speeds because of the increased bandwidth offered by PCIe 4.0.  

The increased bandwidth offered by PCIe 4.0 improves the efficiency of performing workloads, such as machine learning (ML) and cloud computing, reducing the compute time required to complete any given taskAdditionally, it reduces lane congestion and reduces the amount of power consumption used by the device. To sum things up, PCIe offers more performance while reducing the amount of energy required for a given workload.  

PCIe 4.0 vs. PCIe 3.0 (What are the Differences Between PCI Express Gen 4 vs Gen 3?) 

The major difference between PCI Express 4.0 and PCI Express 3.0 is that it doubles the speed of PCIe 3.0, boosting performance from one gigabyte per lane to two gigabytes per lane while providing options for 1x, 2x, 4x, 8x, and 16x slot configurations, increasing the maximum potential bandwidth of a PCI express slot to 64 gigabytes per second. 


 (Photo credit: Microsemi)

That said, current graphics cards are unable to take full advantage of PCIe 4 because they are not even coming close to saturating the bandwidth provided by the PCIe 3 slot. However, where PCIe 4 does shine is when it comes to storage add-in cards.  

For example, PCIe 4.0 NVMe drives will benefit from the added bandwidth because NVMe driveoperating in a Raid 0 configuration are able to perform sequential read/write speeds of up to 15 GB/s. This is crucial for persons and/or organizations performing AI computations using large data sets for training and testing machine learning algorithms because huge data sets need to be stored and fetched repeatedly. 

Overall, PCI Express 4 significantly improves the read/write speeds of SSDs, offering an excellent boost in performance for such complex workloads. As AI algorithms get more and more complex, there will always be a need for faster data transfer speeds. By increasing the available bandwidth, PCIe 4.0 significantly improves the speed at which data can be accessed, providing for smoother real-time data analysis. 

Additionally, PCI Express has the added benefit of reducing the lane requirement for add-in cards. This is so because each of the lanes is becoming faster, reducing the number of lanes required for certain devices.  

For example, an NVMe SSD card can operate at PCIe 4 x8 speeds while enjoying the same bandwidth as a PCIe 3 x16 slots while using half of the lanes. The added lanes can be leveraged for adding additional devices, permitting devices to run using smaller PCIe slots, allowing system builders to build smaller, more compact systems. 

Can You Insert a PCIe Gen 3 Card in a PCIe Gen 4 Slot? 

Yes, you can insert a PCI Express Gen 3 Card in a PCI Express Gen 4 slot because PCI Express 4 is backward compatible with PCI Express 3, meaning older PCI Express devices will properly work if inserted into a PCI Express Gen 4 slot. That said, although older PCI e peripherals will work on a PCIe 4 slot, their speed will be limited to their generation'specifications 

For example, if a PCIe 3.0 graphics card is inserted into a PCIe 4.0 slot, the graphics card would function as if it were inserted into a PCIe 3.0 slot, meaning it would not benefit from being added to PCI Express 4.0 or even a PCIe 5.0 slotThis is so because the specifications of your GPU did not change; it's merely compatible with the new PCIe standard. 

Another example would be connecting a PCIe Gen 3 SSD to a PCIe Gen 4 slot. Even though the PCIe 4 slot is backward compatible with the Gen 3 SSD, the fact that you're connecting it to a Gen 4 slot will not increase data transfer speeds because the SSD'PCIe controller is a Gen 3 controller. So, while compatible, you will not see an increase in performance. 

That said, if you were to connect a Gen 4 PCIe SSD into a Gen 4 slot, you would notice that the PCIe SSD is twice as fast because the system and the SSD support it. You will see an improvement because the data transfer speeds are faster, and the latency to read/write data is also improved. 

Why Do We Need PCIe 4.0? 

We need PCIe 4.0 because as CPUs, GPUs, and data storage devices, such as NVMe SSDs continue to advance, the highways for the data passing among them must improve as well to avoid bottlenecking the system. PCIe Gen 4 improves the amount of bandwidth that's provided for these devices, keeping them satiated with data. 

Take, for example, PCIe M.2 NVMe SSDs. Most M.2 NVMe SSDs utilizthe x4 connection, which has a bandwidth of 4GB/swhich bottlenecks the SSD. However, PCIe Gen 4 increases the bandwidth to approximately 8GB/s, allowing the system to utilize the full potential of the M.2 NVMe drive. As such, it's easy to see that we need PCIe Gen4 to keep up with the advances in computing hardware. 

Additionally, the growth of the internet, the ever-increasing number of IoT devices, and the increasing complexity of AI workload necessitate the need for faster and more efficient interfaces (pipes) through which to transfer data. PCIe Gen satisfies the need by doubling the width of the pipeline. In the future, the need for additional bandwidth will continue to grow to handle the growth in the volume and velocity of data. 

Technological innovations often move faster than market demand, especially as it relates to real-world deployments. A major factor that determines how quickly technology is adopted is the overall total cost of ownership. Even though newer technologies have benefits over pre-existing technology, real-world deployment may not make economic sense because of the cost of deploying new technology and using existing technology. 

The sweet spot for newer technology adoption in many b2b applications is both the economies of scale and a reasonable cost delta between replacing legacy or older technologies that continue to function properly. 

AI edge inference computers


A great example of this case is the introduction of high-performance NVMe storage solutions in manindustry 4.0 or intelligent embedded computing applications. Traditionally many embedded applications in the past relied on the 6Gb/s SATA protocol for its cost but also its performance benchmark of 500 ~ 550 MB/s in transfer speeds.  Even today, many embedded applications are still using the SATA protocol for data storage and transfer of data for local computer storage.  Only recently did NVMe architecture (PCIe Gen 3.0) and storage solutions make a crossover into more embedded computing applications, thanks to the demand for faster processing, storage, and connectivity stemming from edge computing.  

The demand for faster access to high-speed NVMe storage can be seen only recently in Intel’s 8th / 9th gen processors and Q370 chipset architecture and  solutions for the embedded market. These generations of industrial computing solutions specifically dedicate PCIe Gen 3.0 lanes directly for an onboard m.2 NVMe storage solution for access to high-speed storage. Although PCIe Gen 4.0 is available on the market and has theoretically proven benchmarks in performancemany real-world embedded computing applications may not need access to these speeds until a later time in technology adoption.  On the other hand, PCIe Gen 4.0 solutions are proving to be highly beneficial in the high-performance data center environment. 


PCIe Gen 4.0 NVMe SSDs & Data Centers 

We will now explore the benefits that PCIe Gen 4.0 has to offer data centers. 

1. Boost in Data Transfer Speeds 

Although the average PC user will not significantly benefit from PCIe 4.0, data centers will benefit tremendously by switching from PCIe 3.0 to PCIe 4.0. This is so because PCI Express 4.0 makes it possible to move data twice as fast, allowing GPUs and PCIe SSDs to deliver faster I/O, offering a significant performance improvement when performing data-intensive and computational applications such as data analysis, machine learning, and artificial intelligence.  

PCIe Version 4 will result in a performance improvement when performing these tasks because it is able to transfer data at approximately 2GB/s per lane vs. the 1GB/s per lane of PCIe Version 3, thus doubling the performance of the prior generation while providing 4-lane performance of 8GB/s, which is the standard most commonly used by PCIe SSDs. 

When tested, PCIe 4.0 SSDs were able to achieve sequential read speeds of up to 6,900 MB/s and write speeds of up to 4,200 MB/s. On the other hand, PCIe 3.0 SSDs were able to achieve sequential read speeds of up to 3,350 MB/s and sequential write speeds of up t0 3040 MB/s. This shows that PCI Express 4.0 provides a significant performance boost over PCI Express 3.0. 

2. Improvement in Energy Consumption 

The second reason that data centers will benefit from deploying PCIe 4.0 is the added energy efficiency that PCIe 4.0 NVMe SSDs bring to data centers, thus reducing the TCO (total cost of ownership). To measure the energy efficiency of NVMe SSDs, manufacturers measure the rate for each watt of power an SSD consumes.  

One PCI Express Gen 4 NVMe SSD manufacturers demonstrated that it took one watt of electricity to read 276 MB/s. At the same time, PCI Express Gen 3 SSD consumed one watt of electricity to read 134 MB/s of data, providing a 105% increase in energy efficiency over the previous generation. 

The same SSD was tested for power efficiency when writing data. The results showed that it took one watt to write 168 MB/s using a PCIe Gen 4 NVMe SSD, whereas it took a PCIe Gen 3 NVMe SSD one watt to read 121 MB/s, showing that PCIe 4 NVMe SSDs provide a 38% increase in energy efficiency over the previous generation.  

So, not only does deploying NVMe SSDs in data center increase performance, but it also results in better energy efficiency. Although the energy saved by deploying a single PCIe 4.0 NVMe is negligible, when deploying thousands or tens of thousands of these SSDs, you will notice a significant reduction in energy consumption, which translates into lower cost of operation. 

Industrial grade PCIe 4.0 NVMe SSDs are designed and manufactured to run 24/7 in data centers and industrial computers to deliver the maximum amount of performance. So, if you have an application that requires low-latency and blazing fast read/write speeds, PCI Express Gen 4 NVMe SSDs are the best option that is currently available. 

Frequently Asked Questions (FAQs)

1. Is PCIe Gen 4 Worth It?

Although PCIe Gen 4 provides little in advantages in regular applications and use cases, it does offer a significant and noteworthy improvement when it comes to high-performance PCIe NVMe SSDs (solid-state drives) as it allows them to read/write large volumes of data extremely quickly. The benefits of PCIe 4 can best be seen in artificial intelligence and machine learning, where large data sets must be stored and accessed extremely quickly.

2. How Fast is PCIe Gen 4.0?

PCIe has a maximum bandwidth of 64 GB/s as well as 16 GT/s. This translates into 2 GB/s per lane or 64 GB/s in total.

3. Does Intel Support PCIe 4.0?

Intel currently only supports PCIe 3.0; however, Intel has confirmed that it will be adding support for PCIe 4.0 starting in Q1 2021 with the launch of Intel'11th generation Core processors codenamed Rocket Lake.

4. When was PCIe 4 Released?

PCI Express Gen 4 was released in 2017. However, hardware manufacturers have only recently begun implementing the technology into their hardware.

5. What is PCI Express Gen 4 Used For?

PCIe, including PCIe 4.0, is used to connect high-end hardware to computer systems. Hardware that is often plugged into PCIe slots includes GPUs, high-speed NVMe storage, raid cards, capture cards, and memory.