Comparison of PCIe bandwidth and channel number_Key points for selecting M.2 expansion cards

Comparison of PCIe channels and bandwidth: How to buy M.2 expansion cards without wasting them

Published: 2025-09-22 EB-LINK Views: 1533 PCIe channel, bandwidth, M.2 expansion card, server selection

When adding M.2 expansion cards to servers, the most common waste is that the card is fast enough but the slot is not fast enough. Only by clarifying the correspondence between PCIe version, channel number and actual bandwidth can the performance of the expansion card be worthwhile.

First calculate the channel bandwidth of each generation of PCIe

PCIe 3.0 single channel bandwidth is about 1GB/s, x4 theoretical value is about 4GB/s; PCIe 4.0 single channel is about 2GB/s, x4 is about 8GB/s, x8 is about 16GB/s, x16 is about 32GB/s. After deducting the encoding overhead, the actual usability is generally about 90% of the theoretical value. It is recommended to use this conversion when planning capacity and performance, leaving a little margin.

The physical length of the slot is not equal to the number of electrical channels

Full-length x16 slots may only be connected to x4 electrical channels, be sure to check the motherboard manual before installing;
The second x16 often shares the channel with the first, and each is reduced to x8 when full;
The x8 card can be inserted into the x16 slot. Conversely, if the four-port card is inserted into the x8 slot, the four disks can only occupy the bandwidth of two disks;
Channels directly connected to the CPU are generally more stable and have lower latency than those branched out from the chipset.

Match card port number by channel level

When two high-speed NVMe disks each occupy x4, the PCIe 3.0 platform will give priority to the one with more abundant bandwidth.PCI-EX4 to M.2 dual-port expansion card (40G);If you only do data warehousing or backup disks,PCI-EX4 to M.2 dual-port expansion card (20G)More economical. For ideas on storage expansion and network channel allocation in the data center, please refer toData center high-speed interconnection solution.

Remember one sentence when choosing a model: first confirm how many channels the slot can provide, and then decide how many ports the card can provide. If the order is reversed, you will pay for unused bandwidth. If you are not sure about the channel table in the motherboard manual, you can ask EB-LINK technical support to help check, call 0755-83179002.