Output Unit

Output Unit  

• The output unit gets the processed data from the computer and sends it to output devices to make them available to the user of computer.

•  The output data is provided through output devices like display screen, printer, plotter and speaker.

•  The processed data sent to the output device is in a machine understandable form. This processed data is converted to human readable form by the output interface of output device.

In brief, the output unit accepts output data from computer via output device, transforms the
output information to human readable form using the output interface of output device and
provides the transformed output to user. 

Output Devices

Monitor, Visual Display Terminal, Printer, Plotter, Computer Output on Microfi lm
(COM), Video Output System, Audio Response System.

Output devices provide output to the user, which is generated after processing the input data. The
processed data, presented to the user via the output devices could be text, graphics, audio or
video. The output could be on a paper or on a film in a tangible form, or, in an intangible form as
audio, video and electronic form. Output devices are classified as follows—

•  Hard Copy Devices

o Printero Plottero Computer Output on Microfilm (microfiche)

•  Soft Copy Devices

o Monitoro Visual Display Terminalo Video Outputo Audio Response

Hard Copy Devices

The output obtained in a tangible form on a paper or any surface is called hard copy output. The
hard copy can be stored permanently and is portable. The hard copy output can be read or used
without a computer. The devices that generate hard copy output are called hard copy devices.
Printer, plotter and microfiche are common hard copy output devices.

PrinterA printer prints the output information from the computer onto a paper. Printers are generally
used to print textual information, but nowadays printers also print graphical information. The
print quality (sharpness and clarity of print) of the printer is determined by the resolution of the
printer. Resolution is measured in dots per inch (dpi). Printers with a high resolution (more dpi)
provide better quality output. Different kinds of printers are available for different types of
applications. Printers are classified into two categories—impact printer and non-impact printer.Impact printers use the typewriter approach of physically striking a typeface against the paper
and inked ribbon. Impact printers can print a character or an entire line at a time. Impact printers
are low-cost printers useful for bulk printing. Dot matrix printers, daisy wheel printers and drum
printers are examples of impact printers.

Dot Matrix Printers print one i character at a time. The speed of dot matrix
printer lies between 200 and 600 characters per second (cps) and their resolution ranges
from 72 to 360 dpi. Dot matrix printers normally come in two sizes—80 column printer
and 132 column printer. Dot matrix printers can print alphanumeric characters, special
characters, charts and graphs. They can print only in black and white. Some dot matrix
printers can print in both directions - left to right and right to left. Dot matrix printers are
commonly used for printing in applications like payroll and accounting.

dot matrix printer

Daisy Wheel Printers  print one character at a time. They produce letter
quality document which is better than a document printed by a dot matrix printer. The
speed of daisy wheel printers is about 100 cps. The print head of the printer is like a daisy
flower, hence the name. These printers are slow, can only print text (not graphics), and
are costly in comparison to dot matrix printers. Daisy wheel printers are used where high
quality printing is needed and no graphics is needed.

Daisy wheel printer

 Drum Printers are line printers. They are expensive and faster than character printers
but produce a low quality output. They can print 200–2500 lines per minute. Drum
printers are generally used for voluminous print outputs.

Drum printer

Non-Impact Printers  do not hit or impact a ribbon to print. They use electro-static chemicals and

ink-jet technologies. Non-impact printers are faster and quieter than impact printers. They
produce high quality output and can be used for printing text and graphics both in black and
white, and color. Ink-jet printers and laser printers are non-impact printers.

Ink-jet Printers spray ink drops directly on the paper like a jet. Their
resolution is more than 500 dpi. They produce high quality graphics and text. Ink-jet
printers are commonly found in homes and offices.

Ink jet printer

Laser Printers  provide highest quality of text and graphics printing.
Laser printers process and store the entire page before printing and are also known aspage printers. The laser printer can print 5–24 pages of text per minute and their
resolution ranges from 400 to 1200 dpi. They are faster and expensive than impact
printers. Laser printers are used in applications requiring high quality voluminous
printing.

 PlotterA plotter is used for vector graphics output to draw graphs, maps, blueprints of
ships, buildings, etc. Plotters use pens of different colors (cyan, magenta, yellow and black) for
drawing. Plotters draw continuous and accurate lines, in contrast to printers where a line is drawn
as closely spaced dots. Plotter is a slow output device and is expensive. Plotters are of two
kinds—drum plotter and flatbed plotter. In a drum plotter, pens mounted on the carriage are
stationary and move only horizontally; for vertical movement, the drum on which the paper is
fixed moves clockwise and anti-clockwise. In a flatbed plotter, the paper is fixed on a flat bed.
The paper is stationary and the pens mounted on the carriage move horizontally and vertically to
draw lines. Plotters are mainly used for drawings in AUTOCAD (computer assisted drafting),
Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM) applications.

plotter

 Computer Output on MicrofilmA microfilm is in a fiche or roll format, and is used to record computer output
directly from the computer tape or cartridge. Computer Output on Microfilm (COM) is a high
speed and low cost process. It can produce data in microfilm form at a much faster speed from
that of a paper printer. The standard roll film is 16 mm wide with a film image that is 1/24 of the
original document. The copy of the image on microfilm retains its original clarity. Microfilm can
be indexed to facilitate retrieving information from it. For reading images stored on microfilm, a
microfilm reader is used. A screen is used for viewing the enlarged images. COM is suited for
storing large amounts of data for manuals and archive records for long periods of time that have
to be referenced occasionally. COM is used for storing output in banking and insurance
applications, medical X rays, etc.

Microfirm

Soft Copy DevicesThe output obtained in an intangible form on a visual display, audio unit or video unit is called
soft copy output. The soft copy allows corrections to be made, can be stored, and, can be sent via
E– to other users. The soft copy output requires a computer to be read or used. The devices that
generate soft copy output are called soft copy devices. Visual output devices like computer
monitor, visual display terminal, video system and audio response system are common soft copy
output devices.

 MonitorMonitor is a common output device. The monitor is provided along with the computer, to view
the displayed output. A monitor is of two kinds - monochrome display monitor and color display
monitor. A monochrome display monitor uses only one color to display text and color display
monitor can display 256 colors at one time. The number of colors displayed by a color monitor
varies with the kind of color adapter attached to it—CGA, EGA, VGA, XGA and SVGA. The
CGA monitor supports four colors and SVGA supports around 16,000,000 colors. Monitors are
available in various sizes like 14, 15, 17, 19 and 21 inches.
An image on the monitor is created by a configuration of dots, also known as pixels. The clarity
of image on the computer screen depends on three factors—

1. Resolution of Screen—the number of pixels in horizontal and vertical direction. More
the number of pixels, the sharper is the image. The common resolution of computer
screen is 800x600 and 1024x768,
2. Dot Pitch—the diagonal distance between two colored pixels on a display screen, and
3. Refresh Rate—the number of times per second the pixels are recharged so that their glow
remains bright.
Monitors may be Cathode Ray Tube (CRT) monitors that look like a television orLiquid Crystal Display (LCD) monitors that have a high resolution,
flat screen, flat panel display. Nowadays, LCD monitors are generally used.

LCD  Monitor

 Visual Display TerminalA monitor and keyboard together are known as Visual Display Terminal (VDT). A keyboard is
used to input data and monitor is used to display the output from the computer. The monitor is
connected to the computer by a cable. Terminals are categorized as dumb, smart and intelligent
terminals. The dumb terminals do not have processing and programming capabilities. Smart
terminals have built-in processing capability but do not have its own storage capacity. Intelligent
terminals have both built-in processing and storage capacity.

 Video OutputScreen image projector or data projector  is an output device that displays
information from the computer onto a large white screen. The projector is mainly used to display
visual output to a large gathering of people required for the purposes of teaching, training,
meetings, conference presentations, etc. 

 Audio ResponseA complete sound system consists of sound card, microphone, speaker and the appropriate
software. In addition to recording and playing the sound, the software allows editing of sound,
like cutting, copy, amplification and creation of vibrant sound effects.
Audio response provides audio output from the computer. Audio output device like speakers,
headset or headphone  is used for audio output sound from computer. The signals
are sent to the speakers via the sound card that translates the digital sound back into analog
signals. The audio response from the computer may be generated by synthesizing the input
human speech to give audio output, or may be a result of a set of rules that are used to create
artificial speech.
Audio output is commonly used for customer service in airlines, banks, etc. It is also used in
video conferences, surveys, etc. Audio response is used by visually impaired to read information
from the screen. For speech impaired people, audio response helps them to communicate with
other people.