Unix is a portable, multitasking, multiuser, time-sharing operating system (OS) originally developed in 1969 by a group of employees at AT&T. Unix was first programmed in assembly language but was reprogrammed in C in 1973.
Unix has been ported to more machine families than any other operating system. As a result, it has come to be identified with the concept of open systems. Unix operating systems are widely used in PCs, servers and mobile devices. The Unix environment was also an essential element in the development of the Internet and networking.
Unix has a set of concepts that make it unique. For example, Unix uses plain text to store data. It also uses hierarchical file systems and treats devices and certain kinds of inter process communication (IPC) as files.