In Doomsday 2, resources are collected into packages. A package is a folder or a ZIP archive that uses the .pack extension and contains the required metadata that describes the contents of the package.
Doomsday 2 uses an internal file system that abstracts away all platform-specific details about the files being used.
The file system maintains a tree of files and folders. It provides a way to quickly and efficiently locate files anywhere in the tree. It also contains semantic information about the structure and content of the tree, allowing others to know how to treat the files and folders.