This is the Platonic ideal of how computer circuitry is supposed to operate, but engineers have to build actual circuits in the grimy analog world. The hunks of metal and silicon can’t manifest the Platonic behavior shown in those textbooks. Circuits can jump between zero and five volts really, really abruptly but if you monitor them on an oscilloscope, you can see that it’s not a perfectly square wave. Instead you get some thing that looks like this: