Transcript Output Devices - Barbados SDA Secondary

Output Devices
To get processed information
out of a computer, you need
an output device. ‘Output’
means to produce the results
of processed data
The most common types of
output are:
• Soft copy: this is not permanent copy
• It includes output from a computer
monitor, audio (sound) from speakers,
electrical signals from modems and
output from one computer to another.
The most common types of
output are:
• Hard copy: this is also called
permanent output since it is
printed for you to review away
from the computer. Examples are
printed reports and pictures.
Display devices
• Computers display
output on a screen or
monitor.
• Different names have
been used for this
device, including VDT
(video display
terminal), CRT
(cathode ray tube),
Display devices
• VDU (visual display
unit), LCD (liquid
crystal display) flat
screens on laptops
and even LED (lightemitting diode)
screens on palmtop
computers.
How do they work?
• A monitor contains a matrix or array
of luminescent dots of red, green and
blue (known as RGB).
• These can be blended to display
millions of colours. Mapping the
location and colour information of
each bit of data creates a computer
image.
• This is known as a
bitmap (bmp).The
bitmapped image
seen on a monitor is
made up of
thousands of pixels.
Pixel stands for
picture (pix)
element.
Features of a computer screen
• Size
• This is the dimension of the screen which shows
the output. Common desktop screens are from
14 inches to 19 inches measured diagonally.
Larger sizes are now available.
• Resolution
• This determines how clear and detailed the
output on the screen can be. Pictures on a
screen are made up of tiny dots (one dot = 1
pixel). The more pixels per inch, the clearer and
more detailed the graphic.
• Colour
• The number of colours displayed can vary from
16 to 256 to 64 thousand to 16.7 million. The
more colours, the smoother the graphics appear,
especially photos.
• Cursor/pointer
• The cursor is a symbol that shows where you
are working on the screen. It may appear as ~
for text and k for the mouse pointer location.
• Scrolling
• This allows the text or graphic to be moved or up
or down or brought into view on the screen.
Printing devices
• No matter how simple or complex the
data-processing operation is, the final
results must be made available in a
user-friendly form,
• usually in the form of a permanent
record. (hard copy)
Printers
• Printers are devices which output a hard
copy of your work.
• The choice of printer depends on the
speed, quality and quantity you want, and
the cost.
• Two kinds of printer are impact and nonimpact.
Impact Printers
• Impact printers strike through a carbon or
inked ribbon, like a typewriter.
• They are noisy and do not usually print
acceptable graphics.
• However, they are useful for printing
multiple copies using carbon paper.
Train printer
• the characters are located on a
continuous belt.
• The characters move horizontally
across the page and as the required
character moves into position, it is
hammered onto the paper through a
carbon ribbon.
• If the hammer hits a little early or late,
the character will appear slightly to the
right or left of its proper position.
Daisy wheel printer
• The daisy wheel printer uses a wheel with
up to 100 characters.
• Each character is on an individual arm,
and the wheel rotates to bring the required
character into position.
• The hammer hits a single letter,
guaranteeing accurate positioning and
uniform striking.
• This allows fast, quiet and reliable
operation with excellent quality
Dot-matrix printer
• A dot—matrix printer uses pins to print a
pattern of dots on paper. The main
advantages of using matrix printers is the
relatively low cost. The main disadvantage
is the
• relatively poor quality of printing, which
can be read but cannot be used for
reproduction or for business letters.
Line printers
• The characters in line printers are on
a cylinder. Each segment of the
cylinder has the full set of characters
in raised form around its edge.
• One complete line of text is printed
during one revolution of the cylinder.
• All the ‘A’s found in the text on that
particular line are printed first, then all
the ‘B’s, and so on until finally all the
letters that make up the words have
been printed and the line is complete.
• Whereas 200 to 600 lines per minute
maximum are produced by the other
printers, some line printers will
operate at up to 3000 lines per
minute.
Non-impact printers
• These printers do not involve actually
striking the paper.
• Instead, ink spray or toner powder is
used.
• The characters are then fixed onto the
paper by heating, for example.
• Because the printing element is simple
and has no moving parts, these printers
are inexpensive to manufacture and print
quickly and silently
Ink-jet printer
• An ink—jet printer operates by projecting
small ink droplets and deflecting them
electrostatically. Speeds of 4 to 6 pages
per minute may be achieved.
• It is now possible to buy a low-priced,
good quality black-and-white or colour inkjet printer. The quality of printout can be
nearly as good as that of a laser printer,
• Ink-jet printers are slower, their ink filled
print heads have to be cleaned and their
cartridges need to be replaced more
frequently than the toner cartridges of
laser printers.
• Colour ink jet printers are ideal for use at
home, where small-quantity output is
required for greeting cards, photographs
and school work.
• Ordinary paper can be used but for the
best results, particularly in colour, special
glossy paper must be used. This can be
quite costly
Laser printer
• Laser printers produce attractive
documents at a high resolution and are
much faster than ink jets. They are used in
many workplaces because they are quiet,
print quickly,
• can be stocked with a large number of
sheets of paper, and produce very highquality documents.
• The printout from most laser printers tends
to be 300 to 1200 dots printed per inch
(dpi).
• In the laser printer, the paper is charged
electrostatically and attracts dry ink powder. The
pattern is then baked on the paper. Many lines
are printed simultaneously, and speeds of 8 to
12 pages per minute can be attained.
• Colour laser printers are also available. They are
far more costly to buy than a colour ink-jet
printer,
• but produce higher quality images and are
cheaper to run. Some laser printers also perform
the functions of a scanner, a photocopier and fax
machine.
Thermal printers
• Thermal printers use heat on chemically
treated paper to form characters.
• Fax machines and supermarket check out
registers that use rolls of paper are also of
this type.
• Although these printers are quiet, they are
relatively slow, expensive since they
require special paper, cannot use multiplecopy paper, and the print eventually fades.
Plotters
• Car designers, architects and engineers who
wish to print accurate charts, diagrams and 3D
drawings, output not to a laser printer but to a
plotter.
• A plotter uses coloured pens or toner to draw an
image on paper (Fig 1.10).The paper is handled
in different ways depending on the type of
plotter. Flatbed plotters hold the paper
• still while the pens move. Drum plotters roll the
paper over a cylinder, while pinch—roller plotters
are a mixture of the two. The advantage of a
drum plotter is that it can produce very large
drawings.