Unix (officially UNIX) is a computer operating system, like Windows or Macintosh OS. It was first developed by Bell Labs, an AT&T Research Lab, in the late 1960's. An "operating system" is a master program that coordinates other programs' activities and manages files. There are dozens of different implementations of Unix. Different versions are designed to work with different types of hardware. Each version provides a core set of basic Unix commands, but also provides its own unique commands or features. On the i4 machine we use Solaris, a proprietary version of Unix from the Sun Corporation. On the main NYU Web server, we use CentOS, a distribution of Linux.