When the DISPLAY variable is found in the environment upon program startup, WRspice assumes that a graphical (X-window) server is available, and will enable its graphical components. If this initialization fails, WRspice will terminate. If the DISPLAY variable is not set, and the -d option is not used on the command line to specify the display, or the -dnone command line option is given, then WRspice will run in text-only mode. In this mode, the core functionality is available, but not the graphical niceties such as plotting (other than the infamous crude line-printer plots of yore). Under Microsoft Windows, graphics is (of course) always available.