How do direct number operands in a CPU work?
<p>To give an example: a x86_64 CPU reading a 128 bit instruction.</p>

<p>From what I understand, this is centainly a thing that happens in x86 processors.
Otherwise it would not be possible to for instance add a 64-bit number to a 64 bit register (the opcode would take a few bits + 64 bits for the number > 64).</p>

<p>What I would like to know is what the limit of bits in an instruction is and how the instruction is read if it is larger than the bitness (databus).
Besides, I also know most RISC CPU's use a fixed size instruction, so if you pass a number operand directly, does the instruction simply double in size?</p>