The concept of input and output devices is much simpler than it sounds. These devices—most commonly associated with computers—are the basic peripheral hardware you use on a daily basis. Input hardware serves to send data into the computer's CPU, while output devices send data outwards to the user.
Mouse and Keyboard
The two most common forms of input related to computers are the mouse and keyboard. They serve as the gateway of control for the computer. They allow the user to manipulate and dictate tasks—ranging from surfing the Internet to writing documents. Keyboards most commonly come in the form of "QWERTY" keyboards, which have an arrangement that originates from typewriters over a century ago. Mice now come in many types, from traditional cord mice, to wireless and laptop mice.
As humans are visually-focused, the most common output device is the monitor. The monitor visually relays an image, which is created by the computer's operating system. The computer user sends manipulations through input devices, which enter the motherboard and processor, ultimately manifesting themselves in the operating system. Older monitors—much like TVs—have CTRs, or cathode ray tubes. Newer models usually feature LCD screens, which have a greater resolution and are lighter in weight.
Printers and Scanners
Two very similar pieces of hardware perform a closely related function; however, each does the exact opposite of the other one. Printers—an output device—produce images or text from the computer. Scanners, on the other hand, input text and image photos into the computer. A digital representation can then be modified and sent electronically if desired.
Microphone and Speakers
High-quality audio in computers has become more commonplace since the turn of the century. Almost all computers come with built-in speakers; however, you can hook up external speakers as a more enhanced output device—usually through the use of a USB port. Speakers are usually present as an input device; however, they usually have low quality. They allow voice transmission—through the Internet—as well as voice recording.