Windows 10 + Windows 7 Dual Boot

[Sandi1987]

I have installed Windows 10. Can i install Windows 7 on second SSD without loose Windows 10?

 

[Paul NZ]

You could try. Altho it's better if you install the earliest (Win 7 ) first then the latest (Win 8 or 10)

 

[azaran]

Yep very easily actually, I do it regularly for builds in the labs I work in. Load one drive how you want it, yank it and pop in the other drive. Then when you're ready to combine them start playing with the boot loader.

If you want to get in to the nitty grity of it, look in to how to use BCDEdit. It can get a bit complicated at first but once you understand how it works it gets easy.
If you want to do it the easy way and not deal with command line stuff then check out these guys:
http://neosmart.net/EasyBCD/

I prefer doing it over two drives when you want to experiment. If one completely tanks you just have to fix the default bcdedit information which isn't terribly difficult to do.

Remember to back up all your data before you start messing around with it tho.

*Edit just make sure when you do it that the Win10 drive is always your default boot. Win10 gets really picky about not being in control.