Directories, and iterating over files and folders
Improving Node's performance with regards to the filesystem has been one of the main challenges taken up by the core Node team. For example, a (flawed) negative comparison to the Vert.x environment's file serving speed led to some interesting commentary from developers and users of both systems which, while not all constructive, is a good read if one is interested in how filesystems are accessed by Node and other systems: http://vertxproject.wordpress.com/2012/05/09/vert-x-vs-node-js-simple-http-benchmarks/.
Typically, a filesystem groups files into collections, normally referred to as directories. One navigates through directories to find individual files. Once a target file is found, the file object must be wrapped by an interface exposing the file contents for reading and writing.
Because Node development often involves the creation of servers that both accept and emit file data, it should be clear how important transfer speed...
