[kazuya]

Your low level is my high level.

Even assembly code appears high level when you are looking into how the electrons run through silicon and copper. But it's not realistic to cover all the stack down to the atoms. Then which layer you can stop digging at?

For a programmer, the processor architecture (including the instruction set architecture and the bus architecture) level would be fine. It is the strongest abstraction barrier and you rarely need to look below it.

That said, if you are working on embedded systems, knowledge about digital electronics is almost a must, and some analog bits really helps.