If you truly want to understand the x86, you should first learn the 4004, then the 8008, then the 8080, then the 8088, then 8086, then the 80186, then the 80286

If you truly want to understand the x86, you should first learn the 4004, then the 8008, then the 8080, then the 8088, then 8086, then the 80186, then the 80286, then the 80386, then you can go in a number of directions that others have suggested.