The boot loader architecture used by modern versions of Windows was introduced in Windows Vista. The only big change since then was the introduction of (optional) Secure Boot with W8. So, if you're trying to find out what the boot loader related differences are between W7, W8.1 and W10, you need look no further than Secure Boot: https://technet.microsoft.com/en-us/windows/dn168167.aspx
Otherwise the boot loader process is pretty much identical on all of them.