In this chapter we present some of the properties of optical bistability, an effect that is not limited to semiconductors, and some of the concepts of digital optical computing. This concept is based on optical nonlinearities and bi- or multistability. We also explain why digital optical computing did not make its way into broad commercial use. Then we proceed to spintronics and quantum computing. The latter concept especially relies, to a limited extent only, on semiconductor optics. We introduce these ideas here because the author feels that beautiful physics has been accomplished in all three fields, though he also sees strong analogies to the development and the fate of the concept of digital optical computing for the combinations of semiconductor optics with spintronics and quantum computing.