THE OUTPUT UNIT
a. General. The output unit is a device that reports information from computer
storage in a form understood by human beings or another computer system.
Typewriters, printers, card punches, visual display devices, paper tape punches,
magnetic tape units, magnetic disk units, and audio response units are some common
input-output devices: also known as peripherals, machines that provide a
means of communication between different computer systems or between people
b. Impact vs Non-impact Printers. A printer translates electronic signals from
the central processing unit into readable form. The paper output is known as hard copy.
Computer printers are classified by the way they put ink on paper and how nice the
result looks. Other variables are speed, noise, and cost of supplies. To the naked eye,
impact printers seem extremely fast. But the computer has the data available to be
printed and can transfer it to the printer many times faster than the impact printer can
print. This difference between speed of transfer and printing has led to the development
of non-impact printers, a faster method of printing. A non-impact printer does not
require contact between paper and printing head. Instead, an electric charge, heat,
photographic techniques or laser technology is used to print output.
hard copy: the permanent readable copy of a computer output.
c. Buffers. From the beginning, the comparatively slow input and output
equipment has hampered the high speed of the CPU. And so there has been a concern
with improving the speed and efficiency of these devices. Better printers have a buffer,
or built-in memory chip, that improves efficiency by permitting output to be printing after
you exit the program.
buffer: internal storage that holds data read to or from input-output devices.
d. Impact Printers. Some printers. generate a character at a time, others a
character at a time approach.
(1) The dot matrix printer. Dot matrix printers have been the Volkswagons
of personal computing - they are inexpensive and rugged, but can't produce letter-
quality print. They use dot combinations to represent numbers, letters, and special
characters, and have a graphics capability because of the dots. An image is formed
when tiny pins strike an ink ribbon in a matrix of dots. The more pins, the more dots
produced, and the better the quality of the output. A 24-pin machine, for example, will
produce a more professional looking output than a 9-pin model. Most dot matrix
printers can use single sheet paper, but they also make efficient use of continuous--