In the early days, CAD systems consisted of mainframe or mini-computers located in a computer room, linked to so-called “dumb” terminals in the comm center showing text-based information. Today’s systems use a client-server configuration, with data residing on a central computer, physically as small as a PC, linked to workstations that consist of mid-powered PCs. The arrangement allows central storage and retrieval of data, and redundancy in case one workstation stops working. Today’s terminals are 19-inch or larger color models, and the software makes use of color, graphics and symbols to convey information.