Opcodes are stored in the virtual address space of the process. They are simply data, with unique number for each opcode and variation. Parameters - or the actual data to be processed - can reside in other parts of the process address space.
If you open a debugger on a running process and go to memory view, you can see the actual opcodes in the binary section of the process address space. Or, you can dump an executable without running it and view the program as a chunk of memory.
The CPU has instructions to copy data between RAM and registers, and these instructions themselves have their own opcodes.