I need to reinstall Blender but I want to backup my startup file first. Where is this data stored?
When uninstalling (on Windows at least), you don't need to worry about this, Blender will ask you if you want to keep or remove your config files etc, simply choose the former and after reinstalling, your settings will still be there.
Additionally, if you uninstall and the version you are installing is different from the last, press Copy Previous Settings and it will apply your stored config to your fresh install after which you can save as your new default with CtrlU.
The configuration files are:
startup.blend and userpref.blend, bookmarks.txt, recent-files.txt,
The following files are stored in:
%APPDATA% points to
In more recent versions of Windows it will be in:
Note that AppData is a hidden folder, you can change directory to AppData from the command line.
The Linux versions stores the same files at this path
For OS X, the config files can be located at
The Library folder is also likely to be hidden by default so you may have to look up how to unhide it.
I don't know where it is stored, but you could just save your startup file as a normal .blend file, open it in the new blender installation and press CtrlU to set this file as your new startup file.