Computer Output
Contents:
Monitors
Printers
Other Output Devices
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Learning Outcome
Upon completion of this module, readers will be able to:
1. Know the various output devices available nowadays.
2. Distinguish between the various types of printers.
3. Know how to protect themselves from monitors?
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What is Output?
Output is data that has been processed into useful form called information. Computers
generate several types of output, depending on the hardware and software being used
and the requirements of the user.
Four common types of output are:

Text consists of characters; letters, numbers, punctuation marks, or any other
symbol that requires one byte of computer storage space.

Graphics are digital representation of non-textual information such as
drawings, charts and photographs. It could be animated which is created by
displaying a series of still images in rapid sequence. See Figure 1.
Figure 1: Animation.
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
Audio: is music, speech, or any other sound. Recall that sound waves, such as
the human voice or music, are analog. To store such sound, a computer
converts the sounds from continuous analog signal into a digital format. Most
output devices require that the computer convert the digital format back into
analog signals.

Video: consists of images that are played back at speeds that provide the
appearance of full motion. Video often is captured with video input devices
such as video camera. Most video signals are analog; however, some video
device records the video images digitally. A video capture card converts an
analog video signal into a digital that a computer can understand. Some output
devices accept the digital signal.
What are the Output Devices?
An output device is any computer capable of conveying information to a user.
Display Devices
A display device is an output device that usually conveys text, graphics, and video
information. Information shown on a display device often is called soft copy, because
the information exists electronically and is displayed for a temporary period of time.
CRT monitors
A CRT (Cathode Ray Tube) monitor, is a display device that consists of a screen
housed in a plastic or metal case. It consists of a large glass tube. Like a television set,
the core as a CRT monitor is a large glass tube called a cathode ray tube (CRT). The
screen, which is the front of the tube, is coated with tiny dots of phosphor material
that glow when electronically charged. Inside the CRT, an electron beam moves back
and forth across the back of the screen, causing the dots to glow, which produces an
image on the screen. Each dot, called pixel (stands for picture element) is single
point in an electronic image. Monitors consist of hundreds, thousands, or millions of
pixels arranged in rows. See Figure 2 and 3.
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Figure 2: CRT monitor.
Figure 3: CRT electron gun and gun.
The CRT monitors are available in a number of sizes, with the more common being
15, 17, 19, and 21 inches. The size of a monitor is measured diagonally, from corner
to corner. Most monitors are referred to by their viewable size, which is the diagonal
measurement of the cathode ray tube inside the monitor and is larger than the actual
viewing area provided by the monitor. For example, a 17-inch monitor may have a
viewable size of only 15.7 inches. See figure 4.
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Figure 4: The monitor viewable size.
Monitors that display only one color on a black background are considered
monochrome. They are less expensive than color monitors that is why some
organizations use them for applications that do not require color or detail graphics,
such as order entry. Some monochrome monitors use gray scaling, to enhance the
quality of the graphics display. Gray scaling uses many shades of gray from white to
black to form the images.
Flat Panel Displays
A flat-panel display is a lightweight, thin screen that consumes less power than CRT
monitor. Two common types of flat-panel displays are LCD and gas plasma. LCD
displays commonly are used in laptop computers, handheld computers, digital
watches, and calculators because they are thinner and more lightweight than CRT
monitors. While most LCD display is color, some hand held computers use
monochrome LCD displays to save battery power.
Unlike a CRT monitor, an LCD display does not use a cathode ray tube (CRT) to
create images on the screen; it instead uses a liquid crystal display (LCD) as shown in
Figure 5. A liquid crystal display (LCD) has special molecules (called liquid
crystals) deposited between two sheets of material. When an electronic current pass
through, which then creates the desired images on the screen like CRT monitors, the
LCD displays used with laptop computers are available in a variety of sizes, with the
more common being 12.1, 13.3, and 14.1 inches. See Figure 5.
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Figure 5: LCD.
LCD displays produces color using either passive matrix or active-matrix technology.
An active-matrix display uses a separate transistor for each color pixel and thus can
display high-quality color that is viewable from all angles. Active-matrix displays
sometimes are called TFT displays, named after the thin-film transistor (TFT)
technology they use. Because they use many transistors, active-matirx displays
require a lot of power. A passive-matrix display uses fewer transistors and requires
less power, but its color display often is not as bright as an active-matrix display.
Images on a passive-matrix display can be viewable best when you work directly in
front of the display. Passive-matrix displays are less expensive than active-matrix
displays. While LCD displays are used most often with laptops, stand-alone LCD
monitors also can be used with desktop computers.
The term monitor typically is used for desktop display devices, while the term display
is used for display devices on the portable computers. LCD monitors require less
power and take up less desk space than traditional CRT monitors, making them ideal
for users with space limitations. Some LCD monitors even can be mounted on the
wall for increased space savings. Stand-alone LCD monitors, however, are more
expensive than CRT monitors.
Gas Plasma Monitors
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This monitor can measure more than 42 inches and hang directly on a wall, that is
why the large business users prefer it. These monitors use gas plasma technology,
which substitutes a layer of gas for the liquid crystal material in an LCD monitor.
When voltage is applied, the gas glows and produces the pixel that forms an image. It
is much more expensive than LCD monitors. See Figure 6.
Figure 6: Gas plasma monitor.
Monitor Quality
The quality of a monitor’s display depends on:
1. The resolution which is the number of pixel it can display. For example, a
screen with a 640*480 resolution can display 640 columns and 480 rows of
pixel. A monitor with a higher resolution provides a smoother image. Te
selection of the monitor resolution depends on the application, for example
low resolution is sufficient for applications like word processing, while higher
resolution is needed for graphics applications.
2. The dot pitch is a measure of image clarity. The dot pitch is the vertical
distance between each pixel on a monitor. The smaller the distance between
the pixels, the sharper the displayed image. To minimize eye fatigue, you
should use a monitor with a dot pitch of 0.28 millimeters or smaller; otherwise
the eye will be able to detect the gap between the adjacent pixels. See Figure
7.
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Figure 7: Dot pitch.
3. The refresh rate is the speed that the monitor redraws images on the screen. It
is measured according to hertz, which is the number of times per second the
screen is redrawn. A high-quality monitor will provide a refresh rate of at least
75 hertz.
Some older monitors refresh images using techniques called interlacing, in
which the electron beam draws only half the horizontal lines with each pass
(for example, all odd-numbered lines on the next pass). Because it happens so
quickly, the brain perceives the two images as a single image. Interlacing
originally was developed for monitors with slow refresh rates. Most of today’s
monitors are non-interlaced, and they provide a much better, flicker-free
image than interlaced monitors. Ideally, a monitor’s refresh rate should be fast
enough to maintain a constant, flicker-free image. A slower refresh rate causes
the image to fade and then flicker as it is redrawn, which can cause headaches
for users.
Video Cards
All color monitors are working with video cards, also called graphics cards or video
adapters. It converts digital output into an analog video signal that is sent through a
cable to the monitor, and then the monitor separates the video signal into red, green,
and blue signals. Then the electron guns fire the three color signals to the front of the
monitor (refer back to Figure 3). These three dots are combined to make up each
single pixel.
The number of colors that a video card can display is determined by the number of
bits it uses to store information about each pixel. For example, a 24-bit video card
uses 24 bits to store information about each pixel and can display 16.7 million (which
is 224) colors.
All monitors today support the Super Video Graphics Array (SVGA) standard,
which also supports resolution and colors in the VGA standard. This standard has
been developed to define the resolution, number of colors, and other properties for
various types of monitors. Most video cards are equipped with memory, which is used
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to store information about each pixel. Some use Dynamic RAM (DRAM). Higherquality video cards use Video RAM (VRAM) to improve the quality of graphics.
You can adjust the brightness, contrast, positioning, height, and width of images,
using some buttons (controls) on the front of the monitor. Newer monitors have
digital controls that allow you to fine-tune the display in small increments. Another
advantage of digital controls is you quickly can return to the default settings. Many
monitors have a tilt-and-swivel base, so you can adjust the angle of the screen to
minimize neck strain and reduce glare from overhead lighting (refer to the bottom part
of Figure 2).
How to protect yourself from monitors?
Monitors produce a small amount of electromagnetic radiation (EMR), which is a
magnetic field that travels at the speed of light. Although no solid evidence exists to
prove that EMR poses a health risk, an established set of standards, known as MPR
II, define acceptable levels of EMR for a monitor. All high-quality monitors should
comply with MPR II standards. To protect yourself even further, you should sit at
arm’s length from the monitor because electromagnetic radiation only travels a short
distance. Also, electromagnetic radiation is greatest on the sides and back of the
monitor.
To help reduce the amount of electricity used by monitors and other computer
components, manufacturers developed the ENERGY STAR program. This program
encourages manufactures to create energy-efficient devices that require little power
when they are in use. Monitors and devices that meet ENERGY STAR guidelines
display an ENERGY STAR label (see Figure 8).
Figure 8: Energy Star label.
Printers
It is an output device that produces a hardcopy (printout) of the text and graphics,
which can be printed in portrait or landscape orientation (see Figure 9).
Figure 9: Selection of portrait or landscape orientation.
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Types of printers:
1. Impact Printers
An impact printer forms characters and graphics on a piece of paper by striking a
mechanism against an ink ribbon that physically contacts the paper. Because of the
striking activity, impact printers generally are noisy. Many impact printers do not
provide Letter quality (LQ) which is a quality of print acceptable for business letters.
Many impact printers produce near letter quality (NLQ) print, which is slightly less
clear than letter quality. NLQ impact printers are used for jobs such as printing
mailing labels, envelops, or invoices.
Impact printers also are ideal for printing multipart forms (see Figure 10) because
they easily can print through many layers of paper. Impact printers used in many
factories and at retail counters because they can with stand dusty environments,
vibrations, and extreme temperatures.
Figure 10: Multipart forms.
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a. Dot-matrix Printer
A dot-matrix printer is an impact printer that produces printed images when tiny wire
pins on a print head mechanism strike an inked ribbon. When the ribbon presses
against the paper, it creates dots that form characters and graphics.
Figure 11: Dot-matrix printer.
Most dot-matrix printers use continuous form paper (see Figure 12), in which each
sheet of paper is connected together. The pages generally have holes punched along
two opposite sides so the paper can be fed through the printer. One advantage of
continuous form paper is that it does not have to be changed very often because
thousands of pages are connected together.
Figure 12: Continuous form paper.
The print head mechanism on a dot-matrix printer can contain nine to twenty-four
pins, depending on the manufacture and the printer model. A higher number if pins
mean more dots are printed, which results in higher print quality.
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Figure 13: Dot-matrix printer quality.
The speed of a dot-matrix printer is measured by the number of characters per
second (cps) it can prints. The speed of dot-matrix printers ranges from 50 to 700 cps,
depending on the desired print quality.
b. Line Printer
A line printer is a high-speed impact printer that prints an entire line at a time. The
speed of a line printer is measured by the number of lines per minute (lpm) it can
prints (see Figure 13). This kind of printer is capable of printing up to 3,000 lpm. Line
printers typically use 11*17-inches continuous form paper such as the green bar paper
used to print reports from mainframe computers.
Figure 13: Line printer.
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2. Non-impact Printer
This type of printer forms characters and graphics on a piece of paper without actually
striking the paper. Some printers spray ink, some of them use heat and pressure to
create characters and images. They are quieter than the impact printer because they do
not strike the paper.
a. Ink-jet Printer
It sprays tiny drops of liquid ink onto papers. They use individual sheets of paper
stored in a removable or stationary tray. These printers can produce letter-quality text
and graphics in both black-and-white and color on various materials such as envelops,
labels, transparencies, or paper. See Figure 14.
Figure 14: Ink-jet printer.
Some ink-jet printers require a heavier weight premium paper for better looking color
documents. Because of their reasonable cost and letter-quality print, ink-jet printers
have become the popular type of color printer for home users.
Printer resolution is measured by the number of dots per inch (dpi) a printer can
output. With an ink-jet printer, a dot is a drop of ink. A higher dpi means the drops of
ink are smaller, which provides a higher quality image. Most ink-jet printers have dpi
that ranges from 300 to 1,440 dpi. Printers with a higher dpi are more expensive.
The speed of an ink-jet printer is measured by the number of pages per minutes
(ppm) it can print. Most ink-jet printers print from one to eight ppm. Graphics and
colors print at the slower rate.
The print head mechanism of ink-jet printers contains ink-filled print cartridges, each
with fifty to several hundred small ink holes called nozzles. Each nozzle in the printer
cartridge is similar to an individual pin on a dot-matrix printer. Just as any
combination of dot-matrix pins can be activated, ink can be combination of the nozzle
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to form a character or image on the paper. When the print cartridge runs out of ink,
you simply replace the cartridge. Some printers have two print cartridges: one
containing black ink and the other containing colors.
b. Laser Printers
A laser printer is a high-speed, high-quality non-impact printer. Most laser printers
use individual sheets of paper, but some have trays that can accommodate different
sizes of paper. You also can print transparencies on a laser printer. Laser printers can
print text and graphics in very high quality resolutions, ranging from 300 dpi to 1200
dpi. While laser printers typically cost more than ink-jet printers, they also are much
faster, printing text at speeds of 4 to 30 ppm. Depending on the quality and speed of
the printer, the cost of a black-and-white laser printer ranges from a few hundred to
several thousand dollars. See Figure 15.
Figure 15: Laser printer.
When printing a document, laser printers process and store the entire page before they
actually print it, that is why they called page printers. Storing a page before printing
requires laser printers to have a certain amount of memory. Depending on the amount
of graphics you intend to print, a laser printer can have 200 MB of memory or higher.
To print a full-page 600dpi picture, for instance, you might need 8MB of memory on
the printer.
Operating in a manner similar to a copy machine, a laser printer creates images using
a laser beam and powered ink, called toner, which is packaged in a cartridge. The
laser beam produces an image on a special drum inside the printer. The light of the
laser alters the electrical charge on the drum wherever it hits. When this occurs, the
toner sticks to the drum and then is transferred to the paper through a combination of
presser and heat. When the toner runs out, you can replace the toner cartridge. See
Figure 16.
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Figure 16: Laser printer from inside.
c. Plotters and Large-Format Printers
Plotters and larger-format printers are sophisticated printers used to produce highquality drawings such as blueprints, maps, circuit diagrams and signs. These printers
typically can handle paper with widths up to 60 inches. Some plotters and largeformat printers use individual sheets of paper, while others take large rolls. These
printers are used in specialized fields such as engineering, drafting, and graphics art
and usually are very costly. See Figure 17.
Figure 17: Plotter.
Special-Purpose Printer
In addition to the printers just discussed, other printers have been developed for
special purposes. A snapshot printer is a color printer designed to produce photo lab
quality pictures from any image that has been scanned or taken with a digital camera.
See Figure 18.
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Figure 18: Snapshot printer.
A label printer is small printer that prints on an adhesive-type material that can be
placed on a variety of items such as envelops, disks, audio cassettes, photographs, and
toys. Many label printers are used to print bar codes. See Figure 19.
Figure 19: Label printer.
Other Output Devices
Audio Output
Audio is speech, music, or any other sound. Audio output devices are the
components of a computer that produce sounds. Most personal computers have a
small internal speaker that usually outputs only low-quality sound. For this reason,
many personal computer users add higher-quality stereo speakers to their computers.
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The speakers (see Figure 20) are connected to ports on the sound card. Most speakers
have tone and volume controls so you can adjust these settings. If you are in a
computer laboratory or some other crowded environment, speakers might not be
practical; instead, you can plug a headset into a port on the sound card. With the
headset (see Figure 21), only you can hear the sound from the computer.
Figure 20: Speakers.
Figure 21: Headset.
Data Projectors
It takes the image that displays on a computer screen and projects it onto a screen so
that an audience of people can see the image clearly. Data projectors can be large
devices attached to a ceiling or wall in an auditorium, or they can be small portable
devices. See Figure 22 and 23.
Figure 22: LCD Projector.
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Figure 23: LCD Projector.
Exercises: (Try yourself then check the answers below. Note that some questions
require you to refer to other resources. Some answers are not provided.)
1. Compare between CRT and LCD monitors in terms of quality, resolution, price,
and applications.
2. 17-inch monitor is measured (select one):
a. Vertically
b. Horizontally
c. Diagonally
3. Explain the following terms:
a.
b.
c.
d.
e.
Dot pitch
Resolution
Drum
dpi
SVGA
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