3. Encoding The Opcodes, Cont.

• For example, on the x86 CPUs the opcodes for

      mov eax, ebx    ; copy data from EBX register to EAX register
  

  and

      mov ecx, edx    ; copy data from EDX register to ECX register
  

  are different, but both instructions are related: they both move data from one register to another.

• The only difference between the two MOVs is the source and destination operands.

• This suggests that we could encode instructions like MOV with a sub-opcode and encode the operands using other bits within the opcode.