-First off let me say that the keyboard comes in two formats. You will find mechanical and membrane formats out there. Most of you will use and are using the mechanical format.
Mechanical- the keys are mounted on a post along with a spring under the keys. Now you know why they pop back up. One of the primary reasons the mechanical is so popular is they are cheap to make.
Membrane- Instead of a mechanical mechanism it uses a conductive membrane. When membrane is depressed this will send signal to keyboard controller then onto the PC. This type keyboard you might see at work or a construction company. This is usually protected by plastic and incased so that debris doesn’t get in. Another reason for this keyboard is for those company's out there that don’t want a chance of sparks. This would be handy in a refinery but then again most newer keyboard would have a hard time sparking as is.