Hold on. It happened to me: One of my computers didn’t start up and I was afraid I’d lost over 5,000 recent photos which I knew I had not saved on another disk than the only C disk of the broken computer.
Usually I keep copies of data files on several computers, but I admit I’m not very organized at this. So it happens that I have duplicate content on several hard disks and some files on only one disk.
I need a program like the Good Old Norton File Manager (Not sure it was earlier or later than Norton Commander. It stems from the very early Windows versions. Took over from ye old PCTools and I have used it throughout many windows versions up and including XP SP2… Actually my main computer is still running XP.
I’m using Total Commander which isn’t bad but a bit anti intuitive.
But the best value thusfar is in my view: free file sync