Input and Output Devices
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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.
The 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.
INPUT DEVICES
1. Keyboard
(pc keyboard ,you have one in front of you that you can see
for a closer look )PC Keyboard (you
have one in front of you that you can see for a closer look)
The
computer keyboard is used to enter
text information into the computer, as when you type the contents of a
report. The keyboard can also be used to type commands directing the computer
to perform certain actions. Commands are typically chosen from an on-screen
menu using a mouse, but there are often keyboard shortcuts for giving these
same commands.
In addition to the keys of the main keyboard (used for typing
text), keyboards usually also have a numeric keypad (for entering numerical
data efficiently), a bank of editing keys (used in text editing operations),
and a row of function keys along the top (to easily invoke certain program
functions). Laptop computers, which don’t have room for large keyboards,
often include a “fn” key so that other keys can perform double duty
(such as having a numeric keypad function embedded within the main keyboard
keys).
Improper
use or positioning of a keyboard can lead to repetitive-stress injuries.
Some ergonomic keyboards are designed
with angled arrangements of keys and with built-in wrist rests that can
minimize your risk of RSIs.
Most
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.
2.
Pointing Devices
The
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 aserial 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).
3. Mouse
( TWO- BUTTON MOUSE WITH SCROLL WHEEL )
10. Graphics tablet
A
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).
11.
Scanners
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 page's contents.
12. Microphone
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.
13.
MIDI Devices
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).
( MIDI DEVICES )
Output Devices
1. CRT Monitor
The
traditional output device of a personal computer has been the CRT (Cathode
Ray Tube) monitor. Just like a television set (an older one, anyway) the CRT
monitor contains a large cathode ray tube that uses an electron beam of
varying strength to “paint” a picture onto the color phosphorescent dots on
the inside of the screen. CRT monitors are heavy and use more electrical
power than flat panel displays, but they are preferred by some graphic
artists for their accurate color rendition, and preferred by some gamers for
faster response to rapidly changing graphics.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 resolutionof
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.Your 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. Many 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
(CRT
Monitor)
2. 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.
Flat
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.
As
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 the
display.
3. Ink Jet Printer
For
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 color ink 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.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.
4. Laser Printer
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.
Most
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 pages.
5. Other Printers
Multi-function
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 printers can).
6. Sound Output
Computers
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.
Multimedia is
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 graphic..
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waLLiNSiDe
pengenalan kepada sistem komputer
Khamis, 22 Ogos 2013
INPUT AND OUTPUT DEVICES
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