System Output Devices
System Output Devices
A monitor, or visual display unit, is an electronic visual display for
computers. It is now common for a single computer to have multiple
monitors. Currently, most monitors are backlit LCD (flat panel liquid
crystal) displays, which use much less energy than the
olderCRT (Cathode Ray Tube) displays. CRTs aim a stream of electrons
through a mask at a phospher coated, fluorescent screen creating a bright,
sharp image, and much more electromagnetic radiation and heat.
The image is created from approximately one million
(1000x1000) pixels,
or picture
includes subpixels for the primary colors (red, green & blue) which are
mixed to create a color on the screen. You will recall that a true
color display provides approximatley 16 million colors (using one byte
each for the red, green & blue subpixels).
LCD monitor. Note
profile and greatly
improved viewing
monitor. Note
Multiple monitors
allows up
to nine
Monitor performance characteristics
The performance of a monitor is measured by the following parameters:
Luminance, or over-all brightness, is measured in candelas per
square meter (cd/m2 also called a Nit).
Aspect ratios is the ratio of the horizontal length to the vertical
length. Monitors usually have the aspect ratio 4:3, 16:10 or 16:9.
Viewable image size is usually measured diagonally, but the
actual widths and heights are more informative since they are not
affected by the aspect ratio in the same way. For CRTs, the
viewable size is typically 1 in (25 mm) smaller than the tube
Display resolution is the number of distinct pixels in each
dimension that can be displayed. Maximum resolution is limited
by dot pitch.
Dot pitch is the distance between subpixels of the same color in
millimeters. In general, the smaller the dot pitch, the sharper the
picture will appear.
Refresh rate is the number of times in a second that a display is
illuminated. Maximum refresh rate is limited by response time.
Response time is the time a pixel in a monitor takes to go from
Individual pixels
Dot Pitch & Pixels
active (black) to inactive (white) and back to active (black) again,
measured in milliseconds. Lower numbers mean faster transitions
and therefore fewer visible image artifacts.
Contrast ratio is the ratio of the luminosity of the brightest color
(white) to that of the darkest color (black) that the monitor is
capable of producing.
Power consumption is the amount of energy needed (measured
in Watts).
Viewing angle is the maximum angle at which images on the
monitor can be viewed, without excessive degradation to the
image. It is measured in degrees horizontally and vertically.
CRT in the middle of
creating an image (showing
scan line)
Electronic Paper [src]
Electronic paper, e-paper and electronic ink are a range of display
technologies which are designed to mimic the appearance of ordinary ink
on paper. Unlike conventional backlit flat panel displays, electronic paper
displays reflect light like ordinary paper. Many of the technologies can
hold text and images indefinitely without using electricity, while allowing
images to be changed later. Flexible electronic paper uses plastic
substrates and plastic electronics for the display backplane.
Electronic paper is often considered to be more comfortable to read than
conventional displays. This is due to the stable image, which has no need
to be refreshed constantly, a wider viewing angle, and that it reflects
ambient light rather than emitting its own light. An ideal e-paper display
can be read in direct sunlight without the image appearing to fade. The
contrast ratio in available displays as of 2008 might be described as
similar to that of newspaper, though newly-developed displays are
slightly better. There is ongoing competition among manufacturers to
provide full-color ability.
Printing Technology [src]
Printers are routinely classified by the printer technology they employ;
numerous such technologies have been developed over the years. The
choice of engine has a substantial effect on what jobs a printer is suitable
for, as different technologies are capable of different levels of image or
text quality, print speed, cost, and noise. In addition, some printer
technologies are inappropriate for certain types of physical media, such
Electronic paper: Light and
shadow on an Irex iLiad ebook
Kindle 3 Microcapsules
as carbon paper or transparencies.
Sample checks with stubs
A second aspect of printer technology that is often forgotten is resistance
to alteration: liquid ink, such as from an inkjet head or fabric ribbon,
becomes absorbed by the paper fibers, so documents printed with liquid
ink are more difficult to alter than documents printed with toner or solid
inks, which do not penetrate below the paper surface. (This is important
in many financial and business applications.)
Toner-based printers
A laser printer rapidly produces high quality text and graphics. As with
digital photocopiers and multifunction (print, copy, fax) printers, laser
printers employ axerographic printing process but differ from analog
photocopiers in that the image is produced by the direct scanning of a
laser beam across the printer's photoreceptor.
Another toner-based printer is the LED printer which uses an array of
LEDs instead of a laser to cause toner adhesion to the print drum.
Liquid inkjet printers
An image is "written" onto
the photoreceptive drum in a
laser printer
Inkjet printers operate by propelling variably-sized droplets of liquid or
molten material (ink) onto almost any sized page. They are the most
common type of computer printer used by consumers.
Solid ink printers
Solid ink printers are a type of thermal transfer printer. Rather than
mixing red, green and blue, they use solid sticks of CMYK-colored ink,
similar in consistency to candle wax, which are melted and fed into a
piezo crystal operated print-head. The printhead sprays the ink on a
rotating, oil coated drum. The paper then passes over the print drum, at
which time the image is transferred, or transfixed, to the page. Solid ink
printers are most commonly used as color office printers, and are
excellent at printing on transparencies and other non-porous media. Solid
ink printers can produce excellent results. Acquisition and operating costs
are similar to laser printers. Drawbacks of the technology include high
energy consumption and long warm-up times from a cold state. Also,
some users complain that the resulting prints are difficult to write on, as
the wax tends to repel inks from pens, and are difficult to feed through
automatic document feeders, but these traits have been significantly
reduced in later models. In addition, this type of printer is only available
from one manufacturer, Xerox.
Dye-sublimation printer
A dye-sublimation printer is a printer which employs a printing process
that uses heat to transfer dye to a medium such as a plastic card, paper or
Fusing image on laser printer
Grey 'S' made by inkjet printer
(note resolution)
canvas. The process is usually to lay one color at a time using a ribbon
that has color panels. Dye-sublimation printers are intended primarily for
high-quality color applications, including color photography; and are less
well-suited for text. While once the province of high-end print shops,
dye-sublimation printers are now increasingly used as dedicated
consumer photo printers.
Inkless printers
Thermal printer
Thermal printers work by selectively heating regions of special heatsensitive paper. Monochrome thermal printers are used in point of
sale devices, such as, cash registers, ATMs, and gasoline dispensers.
Colors can be achieved with special papers and different temperatures
and heating rates for different colors; these colored sheets are not
required in black-and-white output.
Xerox solid ink sticks
RGB dye sublimation panels
before and after use showing
wasted dye and potential
privacy problems
Sharp thermal printer
Samsung SCX-6320F Multifunctional Laser Printer
Epson MX-80 dot matrix
printer – impact printers are still
used for carbon copies
3 Dimensional Printers
3 D printers became widely available in 2010, but are still quite pricey.
They create solid objects from various materials (e.g., plastic) by adding
layers of the material on top of each other to create the third dimension
(i.e., depth). They are widely used in manufacturing for creating a
prototype of the end product. Automobile manufacturers even use them
to test new design ideas!
3D printer at Makers Party
Computer Speakers ]
Computer speakers, or multimedia speakers, are speakers external to a
computer, that disable the lower fidelity built-in speaker. They often have
a low-power internal amplifier. The standard audio connection is a 3.5
mm (approximately 1/8 inch) stereo jack plug often color-coded lime
green (following the PC 99 standard for computer sound cards). A few
use an RCA connector for input, a plug and socket for a two-wire (signal
and ground) coaxial cable that is widely used to connect analog audio and
video components. There are also USB speakers which are powered from
the 5 volts at 500 milliamps provided by the USB port, allowing about
2.5 Watts of output power.
Computer speakers range widely in quality and in price. The computer
speakers typically packaged with computer systems are small, plastic,
and have mediocre sound quality. Some computer speakers have
equalization features such as bass and treble controls.
Typical external speakers
and connectors (with
The internal amplifiers require an external power source, usually an AC
adapter. More sophisticated computer speakers can have a subwoofer
unit, to enhance bass output, and these units usually include the power RCA connectors (red and white
are for stereo output)
amplifiers both for the bass speaker, and the small satellite speakers.
USB-powered speakers use power supplied through the USB connection.
Some computer displays have rather basic speakers built-in. Laptops
come with integrated speakers. Restricted space available in laptops
means these speakers usually produce low-quality sound.
For some users, a lead connecting computer sound output to an existing
stereo system is practical. This normally yields much better results than
small low-cost computer speakers. Computer speakers can also serve as
an economy amplifier for MP3 player use for those who wish to not use
headphones although some models of computer speakers have headphone
jacks of their own.
USB-powered external
For our purposes, the network (via the NIC) is both an input and an output device for the computer. In
some sense, one could argue that hard disks, DVD reader/writer, and flash drives are I/O devices, except
that these don't involve people. The network often does involve people, e.g., a live webcast or Skype,
which may in turn use speakers, monitors, cameras and microphones.
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