--The instruction set is the lowest level of user-visible software. The instruction set is implemented (in principle) by microcode.
--Microcode (if present) is a bunch of hardwired logic signals that cause data to move between subunits of the CPU in response to instructions. Register transfer specifications govern the design at this level.
--A CPU is a collection of subunits including registers, arithmetic units, and logic gates.
--Registers are collections of flip-flops.
--Arithmetic units are made of logic gates.
--Flip-flops are made from logic gates in feedback configurations to make them stateful. State machine theory governs the design of these circuits.
--Logic gates are stateless and made of transistors. Boolean algebra governs the design at this level.
--Transistors are made of NMOS or PMOS or bipolar silicon junctions. Device physics and electrical properties govern this level.
This abstraction hierarchy is useful when learning, but in the real world the abstraction layers are much blurrier: Everything's really just transistors, stateless stuff often has invisible state, electrical considerations matter at every level, etc.
--The instruction set is the lowest level of user-visible software. The instruction set is implemented (in principle) by microcode.
--Microcode (if present) is a bunch of hardwired logic signals that cause data to move between subunits of the CPU in response to instructions. Register transfer specifications govern the design at this level.
--A CPU is a collection of subunits including registers, arithmetic units, and logic gates.
--Registers are collections of flip-flops.
--Arithmetic units are made of logic gates.
--Flip-flops are made from logic gates in feedback configurations to make them stateful. State machine theory governs the design of these circuits.
--Logic gates are stateless and made of transistors. Boolean algebra governs the design at this level.
--Transistors are made of NMOS or PMOS or bipolar silicon junctions. Device physics and electrical properties govern this level.
This abstraction hierarchy is useful when learning, but in the real world the abstraction layers are much blurrier: Everything's really just transistors, stateless stuff often has invisible state, electrical considerations matter at every level, etc.