Unknown. Help us by suggesting a value.
PCIe slots allow you to connect various components to the motherboard, such as graphics cards and SSDs. The number of data-transmission lanes (specified by the number after the 'x') determines the data transfer rate. PCIe 4.0 provides a 16 GT/s bit rate that doubles the bandwidth provided by PCIe 3.0.
PCIe 4.0 x16 slots: is this important to you?