I have three Windows options; W7, W8.1 and W10. I can use either one of these, and 8.1 is my least favorite. The most important thing is that my programs and games works, but as long as they do work, my most liked Windows versions are in this order: W7 Ultimate (I love it) W10 Home (It's okay) W8.1 Home (I don't like it but I can live with it) All versions are 64-bit. I am now testing out W10, but I may roll back to 8.1 which was preinstalled on this computer. I have an old DVD with W7 Ultimate which I consider installing because I like W7 better. I have too many games to make a list here, there are hundreds. I have got just 3 more weeks to try out W10, so I won't have enough time to test many games. Most games seems to work with W7 and W8.1, but I'm very unsure about W10. Is W10 technically similar to W7 and W8.1 so that if a game did work on the former Windows versions, it will almost always work on W10? For new OS compatibility, does it matter if the games are on DVD or if they are on Steam? I suspect Steam games are more likely to run on new OS but I'm unsure. Half-Life (1) on CD-ROM won't install on Windows 8.1, but the Steam version of the same game does work on both W8.1 and W10. I've got these CIVILIZATION games: Civ II (CD-ROM) Civ III DeLuxe (all three III versions) (CD-ROM) Civ III "Complete" (Steam) Civ IV (all versions/expansion packs) (Steam) Civ V (Steam) I believe I need Win XP to run Civ II, but what about the other Civ games? Do they have problems with some of the Windows versions mentioned?