A description of the historical /usr/tmp was omitted, removing any concept of differences in emphasis between the / and /usr directories. The descriptions of /bin, /usr/bin, /lib, and /usr/lib were omitted because they are not useful for applications. In an early draft, a distinction was made between system and application directory usage, but this was not found to be useful.
The directories / and /dev are included because the notion of a hierarchical directory structure is key to other information presented elsewhere in IEEE Std 1003.1-2001. In early drafts, it was argued that special devices and temporary files could conceivably be handled without a directory structure on some implementations. For example, the system could treat the characters "/tmp" as a special token that would store files using some non-POSIX file system structure. This notion was rejected by the standard developers, who required that all the files in this section be implemented via POSIX file systems.
The /tmp directory is retained in IEEE Std 1003.1-2001 to accommodate historical applications that assume its availability. Implementations are encouraged to provide suitable directory names in the environment variable TMPDIR and applications are encouraged to use the contents of TMPDIR for creating temporary files.
The standard files /dev/null and /dev/tty are required to be both readable and writable to allow applications to have the intended historical access to these files.
The standard file /dev/console has been added for alignment with the Single UNIX Specification.
There is no additional rationale provided for this section.