Addendum: I suppose one way to think about this is to imagine old-school computers. I'm talking about the ones built from TTL logic chips; pre-6502/8080/etc.

Addendum: I suppose one way to think about this is to imagine old-school computers. I'm talking about the ones built from TTL logic chips; pre-6502/8080/etc. ARM is basically selling a virtual "board" with their CPU implemented using those logic chips. You, as the designer, can then connect their board up to other boards to have other functionality you want. A graphics board, a sound board, etc. The difference between those days and today is that these are all virtual. So after you've plugged the boards together a compiler can come through and optimize everything into a final single "board". Which is actually a set of masks used to fab chips on a single piece of silicon. And these boards are somewhat abstractly specified, letting you enable and disable whole portions of it and have the design adapt accordingly (disabling instructions/functionality/etc). This analogy isn't far from the truth, since a netlist is really just a list of logical operations, aka just like TTL logic chips, and their connections. Modern chip development is simply an evolved form of these primordial design techniques. We've replaced manual place and route with "compilers" and optimization algorithms (the original 6502's masks were _hand drawn_. Engineers crawling over a giant plastic sheets making cuts to draw all the transistors and wires). We've replaced manually specifying netlists with higher level languages like Verilog and VHDL. We replaced TTL level CPUs with integrated CPUs. And then eventually replaced whole boards with SoCs. So if you want to learn chip design; start from the beginning; history is very illuminating. Transistors -> TTL logic chips -> 6502/Z80 designs -> SoCs.