After being able to make my flash drive and external hard drive (connected through USB) bootable (for windows installation) and thus changing the device boot order to the USB, I came to the conclusion that the PC will run whatever is in the USB device's root directory by default.
As a result of being curious tho, I removed my internal hard disk drive (the one which has windows installed on it) and connected it through the USB stick, changed the boot order to USB (1st boot) and connected my the drive through the USB cable.
It shows windows windows icon, attempts to boot as it would ever do as an internal hard drive, but after few second a blue screen get shown and restarts and the restart loop continues infinitely.
I was quite curious and would like to ask about how booting from a USB stick works? Why the blue screen? Is the the data to be transmitted too much for a USB a USB device?