Two Versions of Windows on One Hard Drive

I have an older PC with Windows 7, because it's the only OS that will still accept an older Version of Photoshop which I use quite often! I also have another older HP machine running Windows 10, At present I use both machines! I have read that you can load both versions of Windows on one machines hard drive, by putting them on separate partitions, and also there is another way of using software to create a virtual machine! I have read good and bad about both of these methods, so I'm wondering if any members here can tell me if doing this is just a major headache! and if it's even worth doing! And probably most important! Can I even download a copy of Windows 7, Online any longer