1. 'pax' is the POSIX standard archive tool. It supports the two most common forms of standard Unix archive (backup) files - CPIO and TAR. From Mandrake 9.0 RPM

2. Portable Archive Interchange Pax is an archiving utility that reads and writes tar and cpio formats, both the traditional ones and the extended formats specified in IEEE 1003.1. It handles multi-volume archives and automatically determines the format of an archive while reading it. Three user interfaces are supported: tar, cpio, and pax. The pax interface was designed by IEEE 1003.2 as a compromise in the chronic controversy over which of tar or cpio is best. This is the free OpenBSD's version written by Keith Muller. From Debian 3.0r0 APT