In order to use computers for work, we need to give them appropriate input. This input is provided in the form of instructions along with needed data. Any trigger which causes a system to react and perform some activity is called input. When a system receives input it takes that input and does something with it. Typically in a computer, this input is provided by input devices such as a keyboard, mouse, or touch screen. Sometimes this input is also provided by reading files from a computer disk.