I have the old CDs of the game. When I buy it new from GOG, is it possible to play it directly in Win 10. Or do I have to use DOSBox?
THX

I don't think it is possible to play it without Dosbox.
But it comes directly with it so you can just run it and play. (Although it will be most likely necessary to tweak cpu cycles to get correct speed, especially if using high-res)

The last OS where you could play it directly on the OS is Win98. Win98 ran DOS games natively (being basically DOS with an interface on top of it). ME, XP, and beyond are pure Windows so DOS must be emulated there to run. At least, until the source code comes out of hiding (which let's not hold our breath over).