Classification based on PCIe card specifications
The specification of a PCIe card is usually expressed by the number of lanes. Generally speaking, PCIe cards come in five physical sizes: x1, x4, x8, x16, and x32. (PCIe x32 is very rare and not the mainstream specification.) The number after the "x" refers to the number of lanes in the PCIe slot, eg a PCIe x4 card means the card has four lanes.
In practical applications, a PCIe card needs to be inserted into a PCIe slot of a host or server, and the slot specification and configuration are the same as the card. However, in the face of situations like slot shortages, PCIe cards can also fit into a wider slot. For example, a PCIe x8 card can be put into a PCIe x16 slot when the PCIe x8 slot is already occupied, but the card will always run in PCIe x8 mode.
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 undergone many adjustments and improvements. PCIe 1.0 was originally released in 2002, and in order to meet the increasing demand for high bandwidth, different versions have been introduced successively. There are currently five different PCIe standards: PCIe 1.0, PCIe 2.0, PCIe 3.0, PCIe 4.0, and PCIe 5.0, with the transfer rate doubling with each 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, with better performance than before Several versions are better. PCIe 6.x is expected to be released around 2021.
It is worth mentioning that all PCIe card versions are backward compatible, which means that any version of PCIe card and motherboard can work in the lowest version mode.
