What are analog and digital in computer science?
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 &quot;signal processing&quot;. When someone says &quot;analog computer&quot;, 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 &quot;analog&quot; means? The word is taken from Greek word &quot;proportional&quot;. 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 &quot;proportional&quot;, 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.