Using 1 hard drive for Mac and Windows?

Question

macOS

Hello.
There is a macbook with a hard drive on which MacOSXElCapitan is installed, you need to install Windows (7 - 10) on this hard drive, but MacOS should also remain installed.
The goal is to use macos on a macbook and windows on another PC.
How can be implemented?
I ask you to immediately close the conversations about the fact that it is easier to buy a second hard drive, why do you need it - this will not help me in any way.

Answer 1

Reduce partition with macOS
Create a partition for Windows on free space.
Install Windows.
Everything.
Detailed instructions go like this:dual boot mac windows

Answer 2

bootcamp yuzay, mayakovskaya utility

Answer 3

MacOS has a built-in utility that allows you to implement this procedure.
Split partitions through disk utility, then install Windows