Installing Windows 10 and Ubuntu 19 on ASRock X470 Taichi

Motherboard: ASRock X470 Taichi


Drives:
1. Ultra M.2 Socket/PCIe Gen3x4 (Up to 32Gb/s): ADATA XPG SX8200 Pro 1TB,  Sequential read/write speed up to 3500/3000 MB/s

2. M.2 Socket/PCIe Gen2x4 (Up to 20Gb/s): Intel SSD 660p Series 1TB, Sequential read/write speed up to 1800/1800 MB/s


OS Installation:
1. Install Windows 10 on ADATA XPG, full format
2. In BIOS, set Intel SSD 1st boot. You must select it in BBS Prioties first.
3. Install Ubuntu 19 on the Intel SSD drive.
4. In BIOS, set ADATA XPG as the 1st boot drive again.
5. Reboot the machine and you get the GRUB OS loader to select Unbuntu or Windows 10.


Comment:
I am not sure why this worked. When I had set ADATA as the 1st boot drive then installed Ubuntu on Intel SSD, then it didn't work.