Some links of GRUB

https://blog.csdn.net/humanof/article/details/100726977

https://blog.csdn.net/liu5320102/article/details/54846426

https://www.cnblogs.com/f-ck-need-u/archive/2017/06/29/7094693.html

 

boot.img by hard-coded to find core.img, core.img can identify the file system, it will find /boot/grub/grub.cfg, then read a list of operating systems. I can only understand.