> You can't have both programs on your system That's incidental and not by principle, isn't it? You should be able to have a multiple versions of a library ins

> You can't have both programs on your system That's incidental and not by principle, isn't it? You should be able to have a multiple versions of a library installed, and the dynamic linker would pick the appropriate version. Heck you could even have multiple versions in the same process (if you depend on A and B, and B uses an older version of A internally). Unfortunately I think the current dynamic linker on Linux has a shared namespace for symbols. I also disagree that it is not useful to be able to update libraries separately. The example that I like to give is a PyGtk app written against an earlier Gtk2. Without modifications, it ran against the very last Gtk2, but now supporting: Newest themes, draggable menubars, better IME, window size grippers, and all kinds of other improvements to Gtk. In the days of ActiveX (and I realize this is a bad example because in reality you often had breakage), you could update a control and suddenly your app would have new functionality (like being able to read newer file format versions or more options to sort your grids and so on).