A personal computer would be useless if you could not interact with it because
the machine could not receive instructions or deliver the results of its work. Input
devices accept data and instructions from the user or from another computer system (such as a computer on the Internet).
Output devices return processed data to
the user or to another computer system.
Fig. 1: Computer input and output devices.
Computer Input Devices
The most common input device is the keyboard
, which accepts letters
from the user. Another important type of input device is the mouse
which lets you select options from on-screen menus. You use a mouse by moving it
across a flat surface and pressing its buttons. Fig. 1
shows a personal computer with a keyboard, mouse, and microphone.
A variety of other input devices work with personal computers, too: (see Fig. 2
» The trackball
are variations of the mouse
and enable you to draw or point on the screen.
» The joystick
is a swiveling lever mounted on a stationary base that is well
suited for playing video games.
» A scanner
can copy a printed page of text or a graphic into the computer's
memory, freeing you from creating the data from scratch.
» A digital camera
can record still images, which you can view and edit on the
» A microphone
enables you to input your voice or
music as data.
Fig. 2: Varieties of input devices.
Computer Output Devices
The function of an output device is to present
processed data to the user. The most common
output devices are the monitor
and the printer
The computer sends output to the monitor (the
display screen) when the user needs only to see
the output. It sends output to the printer
when the user requests a paper copy
called a hard copy
—of a document.
Just as computers can accept sound as
input, (they can use stereo speakers
as output devices to produce sound
shows a PC with a monitor; printer; and speakers.
Some types of hardware can act as both input and output devices. A touch
screen, for example, is a type of monitor that displays text or icons you can touch.
When you touch the screen, special sensors detect the touch and the computer calculates the point on the screen where you placed your finger. Depending on the location of the touch, the computer determines what information to display or what action to take next.
are the most common types of devices that can perform both input and output. These devices connect one computer to another—a
process known as networking
. The most common kinds of communications devices are modems
, which enable computers to communicate through telephone
or cable television
systems, and network interface cards
(NICs), which let
users connect a group of computers to share data and devices.