Yes, the ISA is a document / specification, not hardware. Implementing all of it correctly is what makes something an x86 CPU, rather than just something with similarities to x86. See the x86 tag wiki for links to the official docs (Intel’s manuals). Intel and AMD’s implementations of the x86 ISA differ mainly in performance, … Read more
x86 is a CISC register machine, where at most 1 operand for any instruction can be an explicit memory address instead of a register, using an addressing mode like [rdi + rax*4]. (There are instruction which can have 2 memory operands with one or both being implicit, though: What x86 instructions take two (or more) … Read more
Addition, subtraction and multiplication are the same provided: Your inputs and outputs are the same size Your behaviour on overflow is wraparound modulo 2n Division is different. Many instruction sets offer multiplication operations where the output is larger than the input, again these are different for signed and unsigned. Furthermore if you are writing your … Read more