and used at several ARPA locations. In the DNLS, overlapping windows were referred to as "display areas" and could store multiple lines of strings.

In 1971, the screen could only be split into two display areas, vertically or horizontally; by early 1973, the full overlapping windowing system was implemented, and was capable of displaying on an Imlac PDS-1. The Xerox Alto greatly improved upon this system by adding the capability to display bitmapped images, buttons,