The root verb in Integral Operating System, meaning ‘to manage, control’.
1606, ‘to be in effect, perform or be at work, exert force or influence’, a back-formation from operation ‘action, performance, work’ (1391), and in part from operātus, past participle of operārī ‘to work’, from PIE base *op- ‘work, produce in abundance’.
Operating system in the computer sense is from 1961.