A multiuser, multitasking 32-bit operating system written in C and developed in the late 1960s at AT&T's Bell Labs. There are many flavors of UNIX: Linux, Solaris, HP-UX, SunOS, FreeBSD, OpenBSD, NetBSD, BSDi, Irix, and many more. UNIX is made up of the kernel, the heart of the operating system, the file system, a hierarchial directory method for organizing files on the disk, and the shell, the user interface which provides the way the user commands the system.