There is a global parameter for the graphics device. The purpose of this global parameter is ostensibly to prevent unnecessary prompting. However, there is an ulterior motive as well. The selection of devices outside of the graphics applications enables us to perform other necessary actions just once.
There is a command for selecting the current graphics device: GDSET. For example,
ICL> gdset xwindows
A selection remains in force until you change it using GDSET again, use NOGLOBALS, or delete the globals file. The current choice can be inspected via the GLOBALS command. If the global parameter is undefined you will be prompted for the device if an application requires it.
You can override the global parameter for the duration of a single application by specifying it by keyword (normally DEVICE=), or in some applications, by position. Here is an example.
ICL> contour device=ps_p
KAPPA --- Kernel Application Package