THE THERMODYNAMICS OF black holes allows one to deduce limits on the density of entropy or information in various circumstances.
The holographic bound defines how much information can be contained in a specified region of space. It can be derived by considering a roughly spherical distribution of matter that is contained within a surface of area A. The matter is induced to collapse to form a black hole (a). The black hole's area must be smaller than A, so its entropy must be less than A/4