If you're looking for configuration for Gnome 2 user applications like Evolution, you'll find it in GConf. Settings are stored in .gconf/ by default (and not normally changed). You can edit the settings using gconf-editor if you want a GTK GUI or using gconftool from the CommandLine.
Comparisons with MicrosoftWindows's registry are inevitable. GConf is a database rather than a series of configuration files, but it's XML, it's open and it actually works.
The Windows registry fails because:
GConf attempts to leapfrog the registry concept. It's a library which provides a simple configuration data storage interface to applications, and also an architecture that tries to make things easy for system administrators.
Here are some of the features of GConf:
This means that programs built from components (where each component may be in a separate process) are much easier to write, because if one component changes a setting the others can discover the change and update themselves. GNOME's Nautilus file manager f.ex. is actually a collection of applications, including an embedded web browser and various navigation components, which communicate via CORBA. However, you want a single preferences dialog located in the top-level "shell" component. Without GConf, a custom protocol would have to be invented for preferences settings to notify embedded components of changes to user preferences.
Notification is also useful if multiple application instances are running. GNOME 2.0 uses this feature to let user interface configuration take effect on-the-fly without restarting any applications; if you turn off toolbar icons, for example, toolbar icons will immediately disappear in all running apps.
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