There is no fundamental difference between symbols inscribed on a stone tablet with a sharp tool versus symbols etched onto a reflective disc by a laser. In both cases you are recording symbolic information on a physical medium; they both record digital information.

The true difference between digital and “analogue” lies in the nature of the representation and interpretation of information, that is whether they are descriptions (symbolic) or analogies. The shape of the groove on a phonograph record is an analogy of a sound wave signal. The pits in a compact disc represent numerals which give a description of the amplitude of a signal at a given point in time.