Back in 16-bit Windows, the registry was a very different beast. Originally, the only registry hive was HKEY_CLASSES_ROOT, and the only things it was used for were COM object registration and file type registration. (Prior to the registry, file type registration was done in WIN.INI, and the only verb you could register for was “open”.) The registry was stored in a single file, REG.DAT, which could not exceed 64KB in size.
Full Post – http://blogs.msdn.com/oldnewthing/archive/2008/01/17/7137438.aspx
