Thin clients have their roots in multi-user systems, traditionally mainframes accessed by some sort of computer terminal. As computer graphics matured, these terminals transitioned from providing a command-line interface to a full graphical user interface, as is common on modern advanced thin clients. The prototypical multi-user environment along these lines, Unix, began to support fully graphical X terminals, i.e., devices running display server software, from about 1984. X terminals remained relatively popular even after the arrival of other thin clients in the mid-late 1990s. Modern Unix derivatives like BSD and Linux continue the tradition of the multi-user, remote display/input session. Typically, X software is not made available on non-X-based thin clients, although no technical reason for this exclusion would prevent it.