Everything is a file describes one of the defining features of Unix, and its derivatives—that a wide range of input/output resources such as documents, directories, hard-drives, modems, keyboards, printers and even some inter-process and network communications are simple streams of bytes exposed through the filesystem name space. Additionally, a range of pseudo and virtual filesystems exists which exposes information about processes and other system information in a hierarchical file-like structure. These are mounted into the single file hierarchy.