A KVM switch is a hardware device that allows a user to control multiple computers from one or more sets of keyboards, video monitors, and mouse.
Mechanical switch for keyboard (serial, PS/2 connector) and video (VGA, DE-15 connector)
A KVM is a computer input/output device offering the combination of a keyboard, video monitor and mouse. They are typically constructed to fit into a 19-inch rack although there are manufacturers who offer a KVM that can be mounted to a flat surface such as a control console.
Rackmount lay-flat KVM
Triple-screen rackmount LCD display