How to install Win8.1 system

under Win10 Install Win10 on Windows 8.1 to form a dual system. But how to install Win8.1 on Windows 10 to form a dual system? Originally brought to Win10 dual system tutorial on Win10.
It is recommended to use the U disk installation method, and support both UEFI and traditional BIOS modes. After downloading the Windows 10 image, install the soft media cube, and find the Rubik's cube in the Rubik's Cube.

According to the tips in the figure, you only need to choose a good USB flash drive (must see carefully, don't choose the wrong one) and mirror, click “ start making & rdquo; you can, if prompted to destroy the U disk data, Please confirm that the U disk is not selected correctly, click OK.
win10 installed win8.1 dual system steps: After entering the setting options, select the boot priority setting option.

Adjust the USB device (Removable Dev.) as the first boot device.