In order for games to create an interactive experience (or even the illusion of interactivity), they must provide some affordance for user input. Input devices and methods have changed significantly over the history of electronic games, typically following a trajectory of increasing bandwidth at the device level and more sophisticated handling of that input at the software level.
While these advances have often appeared in parallel, we have chosen to keep the hardware and software layers of input handling distinct from one another because they can vary independently from one another from game to game. That is, one can vary the hardware device from which a game receives input without altering the game's software. Examples of this are especially apparent when playing games on personal computers. Console emulator software often takes input from the keyboard in formats meant to emulate hardware devices that a PC user may not have. Keyboard input is used in place of a joypad if the player doesn't have that hardware. Similarly, first person shooters provide for input through keyboard and mouse, or through joypads or joysticks. While a player's personal experience using these different interfaces may differ, the ways in which the player's input are handled by the software are not significantly different. A point and click interface works the same at the software level whether using a mouse or joystick. Direct motor control over a player's avatar works the same whether control signals are received through a keyboard, joypad, or fishing controller.
Guitar Hero represents a game with an interesting take on the hardware input; it comes packaged with a toy guitar that plugs into the PS2 and allows the player to interact with the on screen images in an alternative way, due to the hardware input. However, the guitar is essentially just a remapped dual-shock PS2 controller, so the player could presumably play the game with the default controller. This approach, though, alters the game significantly, making it simultaneously less intuitive and more pedestrian; this is a strong example of the hardware mediating the input of the game.