Why is a digital signal better than an analog signal in computing systems?
Great question! Imagine shouting across a canyon. Your voice will bounce around, echo, and possibly be drowned out by the wind. But in that same canyon you could pulse a laser light and get a Morse code message more reliably to the other side, no matter the weather, topography, or day/night cycle.
That canyon represents a very noisy environment. And by noise, I mean any signal that could interfere with and distort the intended messaging signal (wind, for example). Analog signals, like shouting across the canyon, are highly susceptible to noise interference. But shouting is much easier for the sender than having to purchase a laser pointer, so analog signalling is still a low-cost, viable option. There are ways to mitigate the impact of noise on analog signals, like frequency isolation. If there weren't, we wouldn't have radio broadcasts. Still, those broadcasts can be occasionally garbled, and that's an acceptable risk for most people.
But for data transfer in modern computer networks, a garbled transmission is unacceptable. It's worth the extra expense to virtually guarantee successful communication. By converting the signal from continuous waves (like shouting) into a flow of discrete, digital ones and zeros (like Morse code laser pulses), we gain more precision, control, and reliability.
Add glass fiber optics and we remove line-of-sight requirements in that canyon. Add Transmission Control Protocol (TCP) and we can break up the signal into smaller, manageable "packets" that are reassembled on the other end with reliable error management. And add Internet Protocol (IP) addressing and smart routing technology, and you can send a digital signal to any canyon in the world.
Analog signals, even when sent through wires, do not have that kind of reliability.