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A printer can be defined as 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. Larger laser, for example, can print a 400-page manual in a few minutes.
Personal computer printers print only a few pages a minute. Personal computer printers can be distinguished as
dot-matrix, inkjet and laser.
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Dot-matrix: Impact
dot-matrix printers work by striking a series of dots through a ribbon for each printed character. The dot-matrix printer is
still popular in businesses that use carbon copy forms. They require the least
maintenance and ribbons are cheaper than ink or toner cartridges.
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Inkjet: The best-known
non-impact printers are the inkjet printer, of which several manufacturers make. The
inkjet sprays ink from an ink cartridge at very close range to the paper as it rolls by.
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Laser: The laser printer uses a laser beam reflected from a mirror to attract ink dust, called
toner,
to selected paper areas as a sheet rolls over a drum.
The four printer qualities of most interest
to most users are:
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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. Cheap
color printers can hold only one cartridge at a time while more expensive printers can use
two ink cartridges, one color and one black ink.
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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.
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Speed: The average printer
prints out black text anywhere from 3 to 8 sheets per minute. Color printing is slower.
Generally, the more you pay the better performance you will get.
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Memory: Most printers come with a
small amount of memory, about 512 KB to 1 MB. Laser printers can be upgraded. Print
jobs spool to either printer memory or the computer memory. If the job uses the computer
memory performance of further use can be effected until the print job is finished.
Printer I/O Interfaces
The most common I/O interface for printers has been the
parallel Centronics interface
with a 36-pin plug. A USB port is being added to newer printers. The one advantage to a USB printer is that up to 96 USB
devices can be added to your computers without the need
for hardware resource configuration. If you have a lot of devices or want more than one
printer this would be the way to go. Performance is generally better, too.
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 PCL.
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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.
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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
Fonts are 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 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. TrueType and Type
1 fonts are outline fonts. Outline fonts are used with Postscript and PCL printer
languages. |
