Wikipedia
cpio is a general file archiver utility and its associated file format. It is primarily installed on Unix-like computer operating systems. The software utility was originally intended as a tape archiving program as part of the Programmer's Workbench ( PWB/UNIX), and has been a component of virtually every Unix operating system released thereafter. Its name is derived from the phrase copy in and out, in close description of the program's use of standard input and standard output in its operation.
All variants of Unix also support other backup and archiving programs, such as tar, which has become more widely recognized. The use of cpio by the RPM Package Manager, in the initramfs program of Linux kernel 2.6, and in Apple Computer's Installer ( pax) make cpio an important archiving tool.
Since its original design, cpio and its archive file format have undergone several, sometimes incompatible, revisions. Most notable is the change, now an operational option, from the use of a binary format of archive file meta information to an ASCII-based representation.