PCIe (Peripheral Component Interconnect-Express)

An abbreviation for Peripheral Component Interconnect-Express, it is an extended interface standard for high-speed serial transmission.
Since its introduction, it has been upgraded repeatedly, and if you include plans for standardization, Gen1 to Gen6 have appeared as generations.

Assuming that the bidirectional portion of the two differential lines is one lane,
Up to 16 lanes up to Gen2
Gen3 up to 32 lanes
Up to 64 lanes after Gen4
is available.

The transmission speed per lane is
Gen1 = 2.5Gbps
Gen2 = 5.0Gbps
Gen3=8.0Gbps
Gen4=16.0Gbps
Gen5=32Gbps
Gen6 = 64Gbps
and speeding up. As of 2020, practical use is progressing up to Gen4.