[matttheatheist]

   "At the physical level, the 1's and 0's are always voltage levels."

Let me throw you a curve ball: When we're dealing with DIGITAL logic, we're dealing with DISCRETE (and finite) values of SOMETHING - and it doesn't have to always be voltages.

Just to wet your appetite, take a look at "Current-mode circuits". These are circuits whose logic values are represented by discrete current levels, not voltage levels. And by the way, this has Nothing to do with Ohm's Law.

Another example can be taken from digital communications. We have discrete finite levels for: amplitude, frequency, and phase. And I'm probably missing another component that can also be quantized, but it's been many years since I took that class.

Yes, I remember now: Duty Cycle, as used in Pulse Position Modulation and Pulse Width Modulation. These types of modulation are commonly discretized and used in digital communications. Also very common in analog systems.

[roop]

You mean they don't always have to be "voltages". Agreed. I only wanted to emphasize that at the physical level, they are not discrete. In this case, they happen to be represented as voltage drops.

[matttheatheist]

Agreed.

I wish more people would take the time to look at the classic CMOS inverter: Looking at the VIn vs. VOut graph, it is overwhelmingly obvious that the word "digital" refers only to a higher level of abstraction for circuits that, in reality, are analog. (And more to the point, these SAME circuits are used as amplifiers in a typical analog design.)

Good luck explaining this to a CS major.

[roop]

That's funny. I am really a CS guy. Just happened to work for a semiconductor company for a few years after college.