Paul wrote in news
[...]

Yeah I have backups of my data. Online and on a USB if I am going to
delete a partition. I installed win 7. Then shrank and created two
partitions. I installed linux and then on the 3rd partition decided to
try and install 10. Ten didn't take long to install. I was suprised. I
seem to like windows 7 better though. I believe I deleted 10 while in
linux. I don't know you could do it from windows 7. Windows 10 wanted to
repair itself. Interesting setup there. So I rebooted by the wind 7
install disk. repair disk wouldn't do it. And used "fix disk" and the
registry entries were changed.

So I learned some interesting stuff there in this proces. I was given
the options as to booting into 7 or 10. I didn't reinstall grub over
this and put in an option for windows. IDK how that would've worked. I
have learned many thigns from this. And sometimes it has involved losing
data. But what's important I have online backed up. I have found a
reinstall is sometimes only the real way to get rid of some things. You
know these days it's hard to tell what they put on our machines.

Windows 10's booting system intrigues me. It must involve the registry.

Bill