I'll try to answer your remaining question: what are analog and digital in computer science?
The trouble is that these terms aren't from computer science. They are from the field called "signal processing". When someone says "analog computer", they simply mean that the computer is designed on principles of analog signal processing and built from analog components. The same goes for digital computers: they are designed with digital signal processing in mind and built from digital components.
So what does "analog" means? The word is taken from Greek word "proportional". To clarify what it means, let's look at the sum operation implemented with graduated cylinders:
Say you want to compute $13 + 38$. First, you take an empty cylinder and fill it up to $13$ ml mark. Then you take another empty one and fill it up to $38$ ml mark. Then you pour one into the other and look how much ml of liquid is there, which you announce as the result of the sum operation.
This is "proportional", because if you want to use $26$ instead of $13$ as an input, you use double amount of liquid. Double amount of liquid means twice as large number. An electrical analog computer could use the voltage of electric current is a similar way.
Now let's take a look on a digital computation implemented with Soldier Crabs. Here's how you make logical OR:
And here's logical AND:
You put a swarm of crabs where you want logical $1$ as an input and you leave empty places where you want logical $0$. Then you look where the swarm ball ends up and interpret it as $0$ or $1$. This is built on principles of (binary) digital processing:
- No crabs (no electric current, no water flow) means $0$.
- A swarm of crabs (5V, steady water flow) means $1$.
- What if you can't decide which is the case? You just say that your digital component is broken.