What is a PCIe Card?

NADDOD Abel Jan 30, 2023

The PCIe standard was created as the demand for bandwidth, flexibility and performance in network devices increased. Since its introduction in 2001, PCIe has grown rapidly and is widely used in various network devices, of which PCIe card (PCI Express card) is one of the main devices, NADDOD will give a comprehensive introduction to the definition, working principle, advantages and types of PCIe cards through this article.

What is a PCIe Card?

A PCIe card is a network card with a PCIe interface that is used as an expansion port in motherboard-level connections. Specifically, PCIe-based expansion cards plug into PCIe slots in the motherboard of devices such as hosts, servers, and network switches. Most computer motherboards today have dedicated PCIe slots corresponding to PCIe cards, and generally the slots are as wide or wider than the card.

How does a PCIe Card Work?

Unlike a bus that handles data from different sources, a PCIe card can control the flow of data by implementing a series of point-to-point connections through a switch. once the PCIe card is plugged in, a logical connection will be formed between the slot and the card to communicate with each other. This logical connection, called an interconnect or link, supports a point-to-point communication channel between the two PCIe ports and allows them to send and receive common PCI requests or interrupts. As shown in the figure below, the PCIe slot has one/multiple lanes. In the x2 link, each channel contains two different pairs of data transfer sets, one pair for transmitting data and the other pair for receiving data. Therefore, each lane contains a composition of four wires or signal lines.

How does a PCIe Card Work?

Why Choose a PCIe Card?

Before the introduction of PCIe cards, there were two main types of NICs on the market: PCI and PCI-X cards. PCI-E cards have a completely different connector and circuit design, and have improved on the original two mainstream NICs to become one of the most commonly used NICs.

How Many Types of PCIe Cards are There?

There are several types of PCIe cards, and the following will explain the specification and version classification.

Classification Based on PCIe Card Specifications

The specification of PCIe cards is usually indicated by the number of lanes. In general, PCIe cards come in five physical sizes: x1, x4, x8, x16, and x32. (PCIe x32 is very rare and is not a mainstream specification.) The number after the “x” refers to the number of lanes in the PCIe slot, e.g. a PCIe x4 card means that the card has four lanes.

Classification Based on PCIe Card Specifications
In practical applications, a PCIe card needs to be inserted into a PCIe slot in a host or server with the same specifications and configuration as the card. However, faced with a situation like a shortage of slots, a PCIe card can also be installed into a wider slot. For example, in a situation where the PCIe x8 slot is already occupied, a PCIe x8 card can be placed into a PCIe x16 slot, but the card will always operate in PCIe x8 mode.

Classification Based on PCIe Card Versions

PCI Express is a high-speed serial computer expansion bus standard for connecting high-speed components that replaces the older AGP, PCI and PCI- X bus standards and has undergone several tweaks and improvements. PCIe 1.0 was originally released in 2002, and different versions have been released since then to meet the growing demand for higher bandwidth. There are currently five different PCIe standards: PCIe 1.0, PCIe 2.0, PCIe 3.0, PCIe 4.0, and PCIe 5.0, with transfer rates doubling with each passing generation and PCIe 6.0 to be released shortly.

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

It is worth noting that all PCIe card versions are backward compatible, meaning that any version of PCIe card and motherboard will work in the mode of the lowest version. The table below shows the transfer rate comparison between the 5 legacy PCIe versions (in terms of the original version n.0).

Classification Based on PCIe Card Versions

How Do I Choose a PCIe Card?

If you are using a wired network but are not satisfied with a commercially assembled system, then you may want to consider purchasing a PCIe card. Be aware of the prerequisite that your computer must have at least one available PCI Express slot, and the following factors need to be taken into account when purchasing.

PCIe card version and slot width: This is to ensure that the type of PCIe card is compatible with your current device and network environment.

Protocol standards: Before purchasing, you need to determine if the card supports the standards you need, such as RDMA, RoCE, iSCSI, and FCoE.

Controller: Controller chips from Intel, Broadcom, Mellanox and Realtek are the dominant trend.

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


To meet the diverse networking needs, high-end software continues to evolve at an extremely fast pace, which has become the driving force behind the continuous breakthrough in PCIe performance. The latest PCIe 4.x, PCIe 5.x and unlisted PCIe 6.x follow the PCIe standard, and these technologies have proven to close the development gap between PCIe cards and hosts, with endless future potential.