It would all depend on what you mean by from scratch. Let's take a very quick trip down the rabbit hole. If by, from scratch, you simply mean the logical design, then the easiest approach would be to design the your processor using a hardware descriptive language (HDL) such as Verilog or VHDL, and implement it by programming it onto a field programmable gate array (FPGA) using the tool chain of your choice. Even this has vary levels of how 'from scratch' you want to get, depending on what level of abstraction you want to get down to, at the highest level you can simply connect pre-built logical elements like ALUs (Arithmetic Logic Units) and register files with some control circuitry and glue logic, all the way down all of these functional elements 'from scratch' out of individual logic gates (note that there are multiple layers of abstraction between a logic gate and a fully functional ALU. Or if you prefer, instead of using an HDL you could enter the design using a schematic layout package.

If you want to create a custom integrated circuit (IC) you could do that as well. For a relatively modest fee (i.e. several thousand dollars) you could have a chip foundry implement the design for you.

If you want to go deeper still, you could build your own foundry*, but this is likely a very sizable investment, since a modern foundry can cost tens of billions, sure you could probably get by with a more rudimentary set up, but it's still going to be costly. Overall this process is very intensive and expensive, but i encourage you to dig deeper into this subject if its something that interests you. Would you like to know more?
spam fails_task lang_mismatch pii not_appropriate hate_speech sexual_content quality toxicity humor helpfulness creativity violence