You’ll find that everything in IT is about representation. At the end of the day the computer itself is a fluctuating cascade of electrons across sand, or the dripping of fluid through a pipe, or the relative location of gears, cams, and spindles.
Is a really tough question (no, really).
Philosophers have literally wrung each others necks over this topic for millenia.
A Tesla car is a Car. It is also a computer containing a model of the car. Which is real, and which is the representation? the Car, or the model of the Car within the Car?
The Car is obviously physical. When the Car physical changes (such as moving) the model is updated. This would imply that the model is the representation.
When the model of the Car changes, so does the Car. It’s hardly imagined, no pretence need be made. So that would mean the Car is the representation of the computer’s model.
So how to properly think about this?
S Systems are well defined, and well prescribed operations like sorting. There may be many ways to achieve the result, but it is possible to achieve it and it is clear when it is present (or not).
P Systems have a well defined problem, but there is no prescribed means or sufficiently rigorous way to solve it. For example the travelling salesperson problem, or an economic simulation. We know what we want, but there isn’t a way to solve it outside of trying everything (which is impossible), approximating it (which automatically implies the result is wrong for a value of wrongness), or restrict it down to an S system which guarantees results but doesn’t solve parts of the problem.
E systems are emergent systems. They don’t solve the problem, they are part of the problem. Think air traffic controller system. The very act of attempting to solve the problem, changes the problem.
The model and what it represents depends entirely upon the kind of system it sits in.
In the thought experiment the model of the car, and the car are not separate things. Even though part of it is physical.
You’ll find that most textbooks talk about models representing X in the realm of S and P systems.