Messaging

• When you press down a keyboard key, the keyboard sends a signal that is associated with that key. The signal is not the letter or number itself. The operating system translates the signal to a specific character, which is what makes keyboards customizable.
  
  

Keyboard Controller

• Early computers used chips such as the IBM 8042 as keyboard controllers. These chips would receive signals from the keyboards, then pass those signals on to the processor. Modern PCs emulate the functioning of keyboard controllers in their firmware, instead of having physical chips.
  
  

Keyboard Keys

• Each keyboard key effectively acts as a switch that , when activated, completes a circuit and sends its signal. Keys come in two major types: mechanical and membrane. Mechanical keys are spring loaded to be pushed down and allowed to rise back up. Membrane keys have three layers, the top and bottom of which are conductive. When pressed, the two conductive membranes meet through holes in the middle layer and complete the circuit.