We review the behavior of amorphous chalcogenide switching and memory devices, with emphasis on an experiment that measures the acoustic response of a thermophonic cell enclosing an electrically pulsed device. Here the response of the cell is measured simultaneously with the current and voltage versus time profiles. The results clearly demonstrate the fundamentally electronic nature of the switching transition, surprisingly even in thick films. Further, the results concur with a model where the sample heats during the delay time; the heating causes the fields to rearrange and a critical value is reached near an electrode, whereby a carrier generation process is encouraged.It has been almost twenty years since the publication of S.R.