As I mentioned in my previous Dot Net 4 strategy blog entry, we have been thinking about how we want to handle Dot Net 4 from an API and runtime standpoint. Just as a little refresher, remember that when I am talking about a .Net 2 assembly it can actually be any of the .Net 2, 3.0, 3.5 or 3.5 SP1 runtimes. They are a layered cake design in that they all use the same base and build up with additional tiers of functionality. You cannot have a .Net 3.5 app without .Net 2 present, doesn’t exist. It turns out there is an interesting new feature in Dot Net 4 to allow side by side running of managed runtimes within the same application. There is a great CLR Inside Out article online that explains probably way more than I will here, but I wanted to point out a few specific parts of the article and how they impact API writers like VistaDB.