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