In computers, a printer is a device
that accepts text and graphic output
from a computer and transfers the
information to paper, usually to
standard size sheets of paper.
Printers are sometimes sold with
computers, but more frequently are
purchased separately. Printers vary
in size, speed, sophistication, and
cost. In general, more expensive
printers are used for
higher-resolution color printing.
Personal computer printers can be
distinguished as impact or
non-impact printers. Early impact
printers worked something like an
automatic typewriter, with a key
striking an inked impression on
paper for each printed character.
The dot-matrix printer was a popular
low-cost personal computer printer.
It's an impact printer that strikes
the paper a line at a time. The
best-known non-impact printers are
the inkjet printer, of which several
makes of low-cost color printers are
an example, and the laser printer.
The inkjet sprays ink from an ink
cartridge at very close range to the
paper as it rolls by. The laser
printer uses a laser beam reflected
from a mirror to attract ink (called
toner) to selected paper areas as a
sheet rolls over a drum.
The four printer qualities of most
interest to most users are:
• Color: Color is
important for users who need to
print pages for presentations or
maps and other pages where color is
part of the information. Color
printers can also be set to print
only in black-and-white. Color
printers are more expensive to
operate since they use two ink
cartridges (one color and one black
ink) that need to be replaced after
a certain number of pages. Users who
don't have a specific need for color
and who print a lot of pages will
find a black-and-white printer
cheaper to operate.
• Resolution:
Printer resolution (the sharpness of
text and images on paper) is usually
measured in dots per inch (dpi).
Most inexpensive printers provide
sufficient resolution for most
purposes at 600 dpi.
• Speed: If you do
much printing, the speed of the
printer becomes important.
Inexpensive printers print only
about 3 to 6 sheets per minute.
Color printing is slower. More
expensive printers are much faster.
• Memory: Most printers come with a
small amount of memory (for example,
one megabyte) that can be expanded
by the user. Having more than the
minimum amount of memory is helpful
and faster when printing out pages
with large images or tables with
lines around them (which the printer
treats as a large image).
Printer I/O Interfaces
The most common I/O interface for
printers has been the parallel
Centronics interface with a 36-PIN
plug. In the future, however, new
printers and computers are likely to
use a serial interface, especially
Universal Serial Bus or FireWire
with a smaller and less cumbersome
plug.
Printer Languages
Printer languages are commands from
the computer to the printer to tell
the printer how to format the
document being printed. These
commands manage font size, graphics,
compression of data sent to the
printer, color, etc. The two most
popular printer languages are
Postscript and Printer Control
Language.
Postscript is a printer language
that uses English phrases and
programmatic constructions to
describe the appearance of a printed
page to the printer. This printer
language was developed by Adobe in
1985. It introduced new features
such as outline fonts and vector
graphics.
Printers now come from the factory
with or can be loaded with
Postscript support. Postscript is
not restricted to printers. It can
be used with any device that creates
an image using dots such as screen
displays, slide recorders, and image
setters.
PCL (Printer Command Language) is an
escape code language used to send
commands to the printer for printing
documents. Escape code language is
so-called because the escape key
begins the command sequence followed
by a series of code numbers. Hewlett
Packard originally devised PCL for
dot matrix and inkjet printers.
Since its introduction, it has
become an industry standard. Other
manufacturers who sell HP clones
have copied it. Some of these clones
are very good, but there are small
differences in the way they print a
page compared to real HP printers.
In 1984, the original HP Laserjet
printer was introduced using PCL.
PCL helped change the appearance of
low-cost printer documents from poor
to exceptional quality.
Fonts
A font is a set of characters of a
specific style and size within an
overall typeface design. Printers
use resident fonts and soft fonts to
print documents. Resident fonts are
built into the hardware of a
printer. They are also called
internal fonts or built-in fonts.
All printers come with one or more
resident fonts.
Additional fonts can be added by
inserting a font cartridge into the
printer or installing soft fonts to
the hard drive. Resident fonts
cannot be erased unlike soft fonts.
Soft fonts are installed onto the
hard drive and then sent to the
computer's memory when a document is
printed that uses the particular
soft font. Soft fonts can be
purchased in stores or downloaded
from the Internet.
There are two types of fonts used by
the printer and screen display,
bitmap fonts and outline fonts.
Bitmap fonts are digital
representations of fonts that are
not scalable. This means they have a
set size or a limited set of sizes.
For example, if a document using a
bitmap font sized to 24 point is
sent to the printer and there is not
a bitmap font of that size, the
computer will try to guess the right
size. This results in the text
looking stretched-out or squashed.
Jagged edges are also a problem with
bitmap fonts.
Outline fonts are mathematical
descriptions of the font that are
sent to the printer. The printer
then rasterizes (see raster graphics
) or converts them to the dots that
are printed on the paper. Because
they are mathematical, they are
scalable.
This means the size of the font can
be changed without losing the
sharpness or resolution of the
printed text. True Type and Type 1
fonts are outline fonts. Outline
fonts are used with Postscript and
PCL printer languages.
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