What is the difference between the U.2 interface and the SATA E interface

The physical interface of SATA E is actually transformed through the SATA I interface. It uses the SATA I interface and a mini version of the SATA interface with only 4 pins. The small interface can only be connected to the PCI-E line. The advantage of this is that Maintain backward compatibility, because the number of SATA E hard drives is too small at present, or there are several officially commercialized models, so even if the user does not have a hard drive with a SATA Express interface, SATA E can still be used as a 2 SATA I interfaces are used without waste.

The U.2 interface is similar to the SATA E interface in that it uses the existing physical interface as much as possible, but in order to make the bandwidth of the interface faster, it has changed from PCI-E x2 to PCI-E 3.0 x4. Many new protocols are supported, such as NVMe, which are not available in the SATA E interface. It can be considered that U.2 is actually the final form of the evolution of SATA E. 

The device-side interface of U.2 combines the characteristics of SATA and SAS interfaces, and the gap left by the SATA interface is filled with pins in the middle. The L-shaped foolproof design is reserved, so it is compatible with SATA.SAS and SATA E specifications. One end of the motherboard is a miniSAS (SFF-8643) interface, and one end of the U.2 cable on the device end is connected to the SATA power supply, and the - end is connected to the SATA power supply. It is connected to the data port of the U.2 hard disk.