Input and Output Devices
Before a computer can process your data, you need some method to input the data into the machine. The device you use will depend on what form this data takes (be it text, sound, artwork, etc.).
Similarly, after the computer has processed your data, you often need to produce output of the results. This output could be a display on the computer screen, hardcopy on printed pages, or even the audio playback of music you composed on the computer.
terms “input” and “output” are used both as verbs to describe the
process of entering or displaying the data, and as nouns referring to
the data itself entered into or displayed by the computer.
Below we discuss the variety of peripheral devices used for computer input and output.
The computer keyboard is
used to enter text information into the computer. The keyboard can also
be used to type commands directing the computer to perform certain
keyboards attach to the PC via a PS/2 connector or USB port (newer).
Older Macintosh computers used an ABD connector, but for several years
now all Mac keyboards have connected using USB.
graphical user interfaces (GUIs) in use today require some kind of
device for positioning the on-screen cursor. Typical pointing devices
are: mouse, trackball, touch pad, trackpoint, graphics tablet, joystick,
and touch screen.
Pointing devices, such as a mouse, connected to the PC via a serial ports (old), PS/2 mouse port (newer), or USB port (newest). Older Macs used ADB to connect their mice, but all recent Macs use USB (usually to a USB port right on the USB keyboard).
The mouse pointing
device sits on your work surface and is moved with your hand. In older
mice, a ball in the bottom of the mouse rolls on the surface as you move
the mouse, and internal rollers sense the ball movement and transmit
the information to the computer via the cord of the mouse.
The newer optical mouse does
not use a rolling ball, but instead uses a light and a small optical
sensor to detect the motion of the mouse by tracking a tiny image of the
A cordless or wireless mouse communicates with the computer via radio waves (often using BlueTooth hardware and protocol) so that a cord is not needed (but such mice need internal batteries).
A mouse also includes one or more buttons (and possibly a scroll wheel) to allow users to interact with the GUI.
Two-button mouse with scroll wheel
Wireless Macintosh mouse
Most laptop computers today have a touch pad pointing device.
pads have the advantage over mice that they take up much less room to
use. They have the advantage over trackballs (which were used on early
laptops) that there are no moving parts to get dirty and result in jumpy
Touch pad of a PC laptop
Some sub-notebook computers (such as the IBM ThinkPad), which lack room for even a touch pad, incorporate a trackpoint,
a small rubber projection embedded between the keys of the keyboard.
The trackpoint acts like a little joystick that can be used to control
the position of the on-screen cursor.
The trackball is
sort of like an upside-down mouse, with the ball located on top. You
use your fingers to roll the trackball, and internal rollers (similar to
what’s inside a mouse) sense the motion which is transmitted to the
and other game controllers can also be connected to a computer as
pointing devices. They are generally used for playing games, and not for
controlling the on-screen cursor in productivity software.
computers, especially small hand-held PDAs, have touch sensitive
display screens. The user can make choices and press button images on
the screen. We often use a stylus, which you hold like a pen, to “write”
on the surface of a small touch screen.
graphics tablet consists of an electronic writing area and a special
“pen” that works with it. Graphics tablets allows artists to create
graphical images with motions and actions similar to using more
traditional drawing tools. The pen of the graphics tablet is pressure
sensitive, so pressing harder or softer can result in brush strokes of
different width (in an appropriate graphics program).
A scanner is
a device that images a printed page or graphic by digitizing it,
producing an image made of tiny pixels of different brightness and color
values which are represented numerically and sent to the computer.
Scanners scan graphics, but they can also scan pages of text which are
then run through OCR (Optical Character Recognition) software that
identifies the individual letter shapes and creates a text file of the
A microphone can
be attached to a computer to record sound (usually through a sound card
input or circuitry built into the motherboard). The sound is
digitized—turned into numbers that represent the original analog sound
waves—and stored in the computer to later processing and playback.
MIDI (Musical Instrument Digital Interface)
is a system designed to transmit information between electronic musical
instruments. A MIDI musical keyboard can be attached to a computer and
allow a performer to play music that is captured by the computer system
as a sequence of notes with the associated timing (instead of recording
digitized sound waves).
|Magnetic Ink Character Recognition(MICR): :
It is a character recognition technology used primarily by
the banking industry to facilitate the processing of the
cheques. MICR characters ( cheque No., Acc.No.etc) are printed
in special ink usually containing iron oxide. When a document
that contains the ink needs to be read, it passes through a
machine which magnetizes the ink and there will be a reader
sorter unit which translates the magnetic information into
characters. MICR provides a secure, high speed of scanning and
processing information. It scans about 2600 cheques/min.|
The traditional output device of a personal computer has been the CRT (Cathode Ray Tube) monitor.
Monitor screen size is
measured diagonally across the screen, in inches. Not all of the screen
area may be usable for image display, so the viewable area is also
specified. The resolution of
the monitor is the maximum number of pixels it can display horizontally
and vertically (such as 800 x 600, or 1024 x 768, or 1600 x 1200). Most
monitors can display several resolutions below its maximum setting. Pixels (short
for picture elements) are the small dots that make of the image
displayed on the screen. The spacing of the screen’s tiny phosphor dots
is called the dot pitch (dp), typically .28 or .26 (measured in millimeters). A screen with a smaller dot pitch produces sharper images.
computer must produce a video signal that a monitor can display. This
may be handled by circuitry on the motherboard, but is usually handled
by a video card in one of the computer’s expansion slots; often the slot is a special one dedicated to video use, such as an AGP slot (Accelerated Graphics Port). Video cards are also called video display adapters, and graphics cards.
video cards contain separate processors and dedicated video memory for
generating complex graphics quickly without burdening the CPU. These accelerated graphics cards are loved by gamers.
Flat Panel Monitor
A flat panel display usually uses an LCD (Liquid Crystal Display)
screen to display output from the computer. The LCD consists of several
thin layers that polarize the light passing through them. The
polarization of one layer, containing long thin molecules called liquid
crystals, can be controlled electronically at each pixel, blocking
varying amounts of the light to make a pixel lighter or darker. Other
types of flat panel technology exist (such as plasma displays) but LCDs are most commonly used in computers, especially laptops.
Older LCDs had slow response times and low contrast, butactive matrix LCD screens have a transparent thin film transistor (TFT) controlling each pixel, so response, contrast, and viewing angle are much improved.
panel displays are much lighter and less bulky than CRT monitors, and
they consume much less power. They have been more expensive than CRTs in
the past, but the price gap is narrowing. You will see many more flat
panels in the future.
with CRTs, the display size of a flat panel is expressed in inches, and
the resolution is the number of pixels horizontally and vertically on
Ink Jet Printer
Flat panel display (LCD)
hardcopy (printed) output, you need some kind of printer attached to
your computer (or available over a network). The most common type of
printer for home systems is the colorink jet printer.
These printers form the image on the page by spraying tiny droplets of
ink from the print head. The printer needs several colors of ink (cyan,
yellow, magenta, and black) to make color images. Some photo-quality ink
jet printers have more colors of ink.
jet printers are inexpensive, but the cost of consumables (ink
cartridges and special paper) make them costly to operate in the long
run for many purposes.
A laser printer produces
good quality images by the same technology that photocopiers use. A
drum coated with photosensitive material is charged, then an image is
written onto it by a laser (or LEDs) which makes those areas lose the
charge. The drum then rolls through toner (tiny
plastic particles of pigment) that are attracted to the charged areas
of the drum. The toner is then deposited onto the paper, and then fused
into the paper with heat.
laser printers are monochrome (one color only, usually black), but more
expensive laser printers with multiple color toner cartridges can
produce color output.
Laser printers are faster than ink jet printers. Their speed is rated in pages per minute (ppm).
Laser printers are more expensive than ink jets, but they are cheaper
to run in the long term if you just need good quality black & white
printers are available that not only operate as a computer printer, but
also include the hardware needed to be a scanner, photocopier, and FAX
machine as well.
Dot matrix printers
use small electromagnetically activated pins in the print head, and an
inked ribbon, to produce images by impact. These printers are slow and
noisy, and are not commonly used for personal computers anymore (but
they can print multi-layer forms, which neither ink jet or laser
also produce sound output, ranging from simple beeps alerting the user,
to impressive game sound effects, to concert quality music. The
circuitry to produce sound may be included on the motherboard, but high
quality audio output from a PC usually requires a sound card in one of the expansion slots, connected to a set of good quality external speakers or headphones.
a term describing computer output that includes sound, text, graphics,
movies, and animation. A sound card is an example of a multimedia output
device (as is a monitor that can display graphics).