The wonders of CVS include that when you update then the changes you have made to your copy will NOT be overwritten. Rather they will be merged with the changes that have happened in the central repository. If changes centrally have happened in the same place where also you have made changes then CVS will tell you that there has been a conflict and will insert conflict markers. You have to resolve those conflicts by hand. But they don't happen so often. And on Windows there are nice graphical tools to resolve the conflicts, like WinMerge for example.