Differences between USB4 standard and GEN1, Gen2 and Gen3

Before introducing USB4, I have to mention the lightning agreement jointly launched by Intel and apple. Lightning protocol is a combination protocol, which integrates DisplayPort protocol (DP) and PCI Express protocol (PCIe). Lightning 1 and lightning 2 protocols have been launched successively, but the response is mediocre. Later, thunderbolt 3 (tbt3) was introduced, and the transmission speed reached 40Gbps. Later, Intel chose to hand over the protocol to the usb-if Association. In 2019, usb-if integrated lightning 3 protocol (tbt3 for short) on the basis of USB 3.2 and launched USB4 Gen 2x2 and USB4 Gen 3x2. The difference between this renaming and the past is that it still retains the name of USB 3.2. USB4 is doubled based on the original USB 3.2 transmission speed, reaching 40Gbps, that is, the speed of USB4 Gen 3x2. USB4 supports both USB 3.2 and tbt3 transmission. In short, USB4 = USB 3.2 + tbt3. Like USB 3.2, USB4 also has single channel mode and dual channel mode. Like USB 3.2 interface, USB4 interface supports USB PD fast charging protocol.

In a words : Gen refers to the transmission rate. The theoretical transmission rate of Gen2 is 10Gbps, while GEN1 is 5Gbps, usb3.2 gen2x2 is 20gbps, and USB4 gen3x2 is 40Gbps, as shown in the following figure