[EncomLab]

A starting point would be a system that does not require the use of a limited set of pre-defined operations to transform from one state to another state via the interpretation of a set of pre-existing instructions. This rules out any digital system entirely.

[achierius]

But what _would_ qualify? The point being made is that your definition is so constricting as to be useless. Nothing (sans perhaps true physical limit-conditions, like black-holes) would be a black box under your definition.

[EncomLab]

It's really only constricting to state machines which are dependent upon a fixed instruction set to function.