Comment Re:Knuth is right. (Score 1) 149
Electronics are only the substrate on which we (currently) perform (most) computing, not the computer itself. They're not even the first substrate that we've ever used for such things: ENIAC is widely credited as the first all-electric computer, but hybrid electronic-mechanical devices had been in use for several decades before then. Pure mechanical devices have also been used in limited capacities, even if we discount the works of Charles Babbage (since his Analytical Engine was never actually built).
But even mechanical devices are not the only substrate that can be used for computing. For example, fluidics (which replace electronics with flowing fluids of various sorts) see limited application on the macro-scale, but are a growing area of nanotechnology research. We've probably all seen examples of toy "computers" using marbles or billiard balls, and if you haven't then a quick YouTube search can provide some. These aren't fast enough to do many things on a practical time scale (by human standards), but they compute nonetheless.
That's why we say that mathematics defines computing. The actual process can be carried out in a multitude of ways, but the underlying processes are the same, and they are defined by the math of computing.