Printers
provide information in a permanent, human-readable form. They are the most
commonly used output devices and are components of almost all computer
systems. Printers vary greatly in performance and design. Vfe will
classify printers as character printers, line printers and page printers in
order to identify three different approaches to printing, each with a
different speed range. In addition, printers can be described as either
impact or nonimpact. Printers that use electromechanical mechanisms that
cause hammers to strike against a ribbon and the paper are called impact
printers. Nonimpact printers do not hit or impact a ribbon to print.
Character printers print
only one character at a time. A typewriter is an example of a character
printer. Character printers are the type used with literally all
microcomputers as well as on computers of all sizes whenever the printing
requirements are not large. Character printers may be of several types. A
letter-quality printer is a character printer which produces
output of typewriter quality. Letter-quality printers typically have speeds
ranging from 10 to 50 characters per second. Dot-matrix
printers form each character as a pattern of dots. These printers
have a lower quality of type but are generally faster printers than the
letter-quality printers — in the range of 50 to 200 characters per second.
One of the newest types of character printer is the
ink-jet printer. It sprays small drops of ink onto paper to form
printed characters. The ink has a high iron content, which is affected by
magnetic fields of the printer. These magnetic fields cause the ink to take
the shape of a character as the ink approaches the paper.
Line printers are
electromechanical machines used for high-volume paper output on most
computer systems. Their printing speeds are such that to an observer they
appear to be printing a line at a time. They are impact printers. Trie
speeds of line printers vary from 100 to 2500 lines per minute. Line
printers have been designed to use many different types of printing
mechanisms. Two of the most common print mechanisms are the drum and the
chain. Drum
printers use a solid, cylindrical drum, rotating at a rapid
speed. Speeds of dram printers vary from 200 to over 2000 lines per minute. Chain
printers have their character set on a rapidly rotating chain
called a print chain. Speeds of chain printers range from 400 to 2400 lines
per minute.
Page printers are
high-speed nonimpact printers. Their printing rates are so high that output
appears to emerge from the printer a page at a time. A variety of techniques
are used in the design of page printers. These techniques, called
electrophotographic techniques, have developed from the paper copier
technology. Laser-beam
printers use a combination of laser beam and electrophotographic
techniques to create printer output at a rate equal to 18000 lines per
minute. |