What is PCI Express (PCIe)?

The PCI Express card is one of the main devices. This article describes the definition, working principles, advantages, and types of PCIe cards.

Table of Contents

As network devices require more bandwidth, flexibility, and performance, the PCIe standard emerges. Since its introduction in 2001, PCIe has developed rapidly and is widely used in various network devices. The PCI Express card is one of the main devices. This article describes the definition, working principles, advantages, and types of PCIe cards.

▮ What is PCIe Card?

A PCIe card is a network card with PCIe ports and is used as an expansion port for motherboard-level connections. In particular, PCI-based expansion cards can be inserted into PCIe slots on the motherboard of devices such as hosts, servers, and network switches. Most computers today have a dedicated PCIe slot on the host board that corresponds to the PCIe card. Generally, the slot is at least as wide as the card.

How does a PCIe card work?

Unlike buses, which handle data from multiple sources, PCIe cards can control the flow of data across a series of point-to-point connections through switches. After a PCIe NIC is installed, a logical connection is established between the slot and the NIC for communication. This logical connection, called an interconnect or link, supports a point-to-point communication channel between two PCIe ports, allowing them to send and receive normal PCI requests or interrupts. As shown in the image below, a PCIe slot has one or more lanes. On the X2 link, each channel contains two different pairs of transmit data groups, one pair for transmitting data and the other pair for receivingData. Thus each channel consists of four wires or signal lines.

Image from FS community: (How does PCIe work)
Image from FS community: (How does PCIe work)

Why choose a PCIe card?

Before the advent of PCIe cards, there were two main types of network cards: PCI and PCI-X cards. The connector and circuit design of the PCI-E cards are completely different. It has been improved on the basis of the two originals. most important network card and becomes the most used network card.

How many types of PCIe cards are there?

There are different types of PCIe cards. The following describes the specifications and versions of PCIe cards.

Number 1: Category based on PCIe card specifications

PCIe card specifications are usually represented by the number of lanes. PCIe cards generally have five physical specifications: X1, X4, X8, X16, and X32. (PCIe X32 is rare and not a mainstream specification.) The number after X indicates the number of channels in the PCIe slot. For example, a PCIe X4 card will indicate that the card has four lanes.

Image from FS Community (Comparison of PCIe Sizes)

In real applications, insert the PCIe card into the host or server PCIe slot. The specifications and slot configuration are the same as the PCIe card. However, given the slot shortage, PCIe cards can also be installed in a wider slot. For example, when the PCIe X8 slot is occupied, you can insert the PCIe X8 card into the PCIe X16 slot, but the card always works in PCIe X8 mode. Please see the table below for details on the PCIe card specifications.

The Slot WidthPin NumberLength
PCIe x 11825mm
PCIe x 42139mm
PCIe x 84956mm
PCIe x 168289mm

Number 2: Classification based on PCIe card version

PCI Express is a high-speed serial computer expansion bus standard for connecting high-speed components. It replaces the old AGP, PCI, and PCI-X bus standards and has been modified and improved several times. PCIe 1.0 was first released in 2002 and has since been released in various versions to meet the increasing demand for high bandwidth. There are five different PCIe standards: PCIe 1.0, PCIe 2.0, PCIe 3.0, PCIe 4.0 and PCIe 5.0. The transfer rate doubles with each generation. PCIe 6.0 will be released soon.

There are currently five versions of PCIe cards: PCIe 1.x, PCIe 2.x, PCIe 3.x, PCIe 4.x, and PCIe 5. A new version of PCIe 5.x was released in 2019 and offers better performance than previous versions. PCIe 6.x is expected to be released around 2021.

It is worth noting that all versions of the PCIe card are backward compatible, which means that any version of the PCIe card and motherboard will work in the lowest version mode. The table below compares the transfer speeds of five traditional versions of PCIe (using the original N.0 version as an example).

VersionIssue TimeTransmission Rate
(Throughput, x1)
Transmission Rate
(Throughput, x16)
Line Code
PCIe 1.020032.5 GT/s (250 MB/s)40 GT/s (4.0 GB/s)8b/10b
PCIe 2.020075.0 GT/s (500 MB/s)80 GT/s (8.0 GB/s)8b/10b
PCIe 3.020108.0 GT/s (984.6 MB/s)128 GT/s (15.75 GB/s)128b/130b
PCIe 4.0201716.0 GT/s (1969 MB/s)256 GT/s (31.51 GB/s)128b/130b
PCIe 5.0201932.0 GT/s (3938 MB/s)512 GT/s (63.02 GB/s)128b/130b

How to Choose the PCIe Card?

If you use a wired network and are not satisfied with a commercially assembled system, consider purchasing a PCIe card. Please note that your computer must have at least one available PCI Express slot and consider the following factors when purchasing:

  • PCIe card version and slot width: This is to ensure that the PCIe card type is compatible with your current device and network environment.
  • Protocol Standards: Before you buy, determine if your network card supports the standards you need, such as RDMA, RoCE, iSCSI, and FCoE.
  • Controller: Controller chips from Intel, Broadcom, Mellanox, and Realtek are the main trend.

In addition to the three factors mentioned above, transmission speed, number of ports, connector type, operating system, brand, price, and other factors should also be considered.


To meet diverse network needs, high-end software is evolving rapidly, which has become the driving force behind continuous advances in PCIe performance. The latest PCIE4.X, PCIe 5.X, and PCIe 6 have not been released. X adheres to PCIe standards, and these technologies are proven to bridge the gap between PCIe cards and consoles with great future potential.


DiskMFR Field Sales Manager - Leo

It’s Leo Zhi. He was born on August 1987. Major in Electronic Engineering & Business English, He is an Enthusiastic professional, a responsible person, and computer hardware & software literate. Proficient in NAND flash products for more than 10 years, critical thinking skills, outstanding leadership, excellent Teamwork, and interpersonal skills.  Understanding customer technical queries and issues, providing initial analysis and solutions. If you have any queries, Please feel free to let me know, Thanks

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