As the brush enthusiasts understand, if you want to use your third party's ROM for your mobile phone, you must first flash in a third party Recovery, such as TWRP. After that, users can use this third party's Recovery to scan the third party's ROM. The tripartite ROM.
In addition, it should be noted that the user usually needs to unlock the Bootloader of the mobile phone before the third-party Recovery. After unlocking, the user can perform various write operations on the mobile phone.
About data decryption and emptying the whole machine
Newer Android phones have encrypted the user's data. Therefore, if a third-party Recovery wants to flash a third-party flash ROM on a mobile phone, the data must be decrypted first; if Recovery cannot decrypt the mobile phone, it is in the process of flashing. The data of all partitions of the whole machine must be formatted and cleared, instead of only clearing the corresponding system partition.
The release of this Recovery means that users can only flash the system while flashing, without having to erase their photos, music and other media data.