global-set-key in X Windows

[Harter, Douglas]

I am on Solaris Unix system. I use emacs a lot of the time using the X
Windows interface. However, there are times when I cannot use the X Windows
interface because  it is not available at that time.

Is there a way in emacs to find out if I am using the X Windows interface or
not?

I have found that the keys on the auxiliary keypad are defined differently
in X Windows  and non X windows. I would like to check if it is in X-Windows
and set some keys differently if it is not.
.