David's Blague

A computer is a machine made only of switches.  We forget this.  We think in computational metaphors: functions, procedures, objects, monads, functors, generators, routines.  Even low-level ints, bools, chars, and floats obscure the facts from us.  A computer is a machine that knows nothing of language or metaphor: every operation is nothing more than the opening or closing of an electric circuit.

An initial useful abstraction beyond this concrete reality is that some of the switches are controlled indirectly.  They are electrical circuits that can only be opened or closed by the computer itself- they cannot be manipulated directly.  We call these circuits the computer's memory.

A second useful abstraction of our switch-machine is that we can store the process for using it.  Humans have been doing this with machines for at least several hundred years, but beginning around sixty years ago, we began to use the machine itself to store this information.