Well, let's see how many layers of abstraction the Alto has. 1) Software (a BCPL program). 2) Library / OS code. 3) Machine code. 4) Microcode. 5) Logic signals

Well, let's see how many layers of abstraction the Alto has. 1) Software (a BCPL program). 2) Library / OS code. 3) Machine code. 4) Microcode. 5) Logic signals (TTL chips). 6) Analog signals (e.g. rise time and voltage of the logic signals). 7) Transistors inside the chips. 8) Quantum mechanics. (The last two levels are hidden to us.) If you're using Smalltalk, you could add another layer for the interpreter.