The Jargon File (version 4.4.7, 29 Dec 2003):

knobs
 pl.n.

    Configurable options, even in software and even those you can't adjust in
    real time. Anything you can twiddle is a knob. ?Has this PNG viewer got
    an alpha knob?? Software may be described as having ?knobs and switches? or
    occasionally ?knobs and lights?. See also nerd knob