As an application developer, how and where you put the preferences vary depending on your application, the platform it runs on, and the programming language. If your application will run only on Windows, then Registry is the place to put the preferences. Developers writing applications written in portable C/C++, on the other hand, usually put their preferences in files. Bigger, server-side applications might store them in a database (although usually something needs to be stored in a file -- the connection string to the database, for example).