At the lowest level, executable code consists of machine language instructions specific to an individual processor—typically a central processing unit (CPU).
A machine language consists of groups of binary values signifying processor instructions that change the state of the computer from its preceding state.
For example, an instruction may change the value stored in a particular storage location in the computer—an effect that is not directly observable to the user.
An instruction may also (indirectly) cause something to appear on a display of the computer system—a state change which should be visible to the user. The processor carries out the instructions in the order they are provided, unless it is instructed to "jump" to a different instruction, or is interrupted.