I have heard about the BOCHS app which can run a virtual machine created by us on android. So we can run Windows OS on Android (please refer to this link). I want to know that if it's just a virtual machine opened by an app then we can click back button it will close the app and bring us back to the Android screen or it will turn our Android completely to Windows?
No we cant. BOCHS is a single thread program. And till now, individual processor cores aren't that strong for any android till today to run any modern OS as intended.
Infact, even you you managed to install just the os, the hardware wont be enough t or run any app and interface will be far too pain.
You can install older OSes like windows xp (on phones like s5-s6 or similar) or windows 98, but again, no real softwares could be run. Forget games, even mugen doesn't run properly. Even if the android hardware is good enough, BOCHS hasnt developed to that level yet.
So until BOCHS supports multi-threading and some other things, its almost useless to try that. Plus you can install only older OSes. New ones will hang a lot. I have personally tried Ubuntu 12.04 and a stripped off version of windows xp. But they were no use.
The only thing its good for is that you can say "Hey look! I got windows in my phone". But other than that, there's no purpose, atleast for now.
Will running virtual machine on Android completely turn my Android into Windows phone
Its not what you think it is. As I already said, you wont be able to make use of any major function. Its like using virtualisation programs like virtualbox on pc. Your pc wont turn in to that os, but both OSes will run simultaneously. SO no, your android wont be replaced. And android and that OS will both run together until you exit the app. Thats all it is to it.... The article is over-exaggerated. Infact, you will get bored of this in less than a day.
Again, feel free to try.
Finally, its not the os from windows phones. Instead, it is the actual windows we run on pc. You can imagine what it would be like in such a small sized screen like phone right?