Specifications

document overall. However, techniques such as resolution enhancement and interpolation do not
apply to dot-matrix technology, making the resolution of the printer a far less important statistic.
Beyond checking to see whether the printer has 9 or 24 pins, you will not see differences in print
quality that are the result of print resolution technology.
Instead, the freshness of the ribbon and the character set used by the printer are the biggest determi-
nants of a dot-matrix printer’s print quality.
Note
Manufacturers once described 24-pin dot-matrix printers as producing “near letter quality” output. In an era of 600dpi
and higher-resolution laser and inkjet printers, “near letter quality” is no longer accurate. Dot-matrix printers still have their
place in the professional world, such as for printing multipart forms and carbon copies, but when it comes to printing let-
ters and other general office documents, they lack the resolution necessary to produce a professional-looking product.
Although any dot-matrix printer is vulnerable to print head damage (the “pins” are actually fine wires), 24-pin dot-matrix
printers are particularly sensitive to incorrectly set head gaps and worn ribbons. These problems can cause the extra-fine
wires to break, resulting in gaps in the printing. When evaluating dot-matrix printers for heavy-duty printing, find out what
the replacement or repair costs of a print head will be.
Page Description Languages
Both laser and inkjet printers are known as page printers because they assemble an entire page in mem-
ory before committing it to paper; the laser printer assembles the page within its own memory,
whereas most inkjet printers use the computer’s memory to assemble the page. Some high-end print-
ers have large memory buffers onboard, but these are used to receive the documents after assembly by
the computer. This is in contrast to dot-matrix printers, which are character-based. When your PC
communicates with a page printer, it does so using a specialized language called a page description lan-
guage (PDL). A PDL is simply a means of coding every aspect of a printed document into a data stream
that can be transmitted to the printer. After the PDL code arrives at the printer, internal firmware con-
verts the code to the pattern of dots that are printed on the page. Currently, two PDLs are in use
today that have become de facto standards in the computer industry: PCL and PostScript. These lan-
guages are discussed in the following sections.
Printers that do not support a PDL use escape code sequences to control the printer’s features in com-
bination with standard ASCII text for the body of the document (see the section, “Escape Codes,”
later in this chapter). The printer driver loaded on your PC is responsible for producing print output
that is understood by your printer, whether it uses escape codes or a PDL. No matter what the source
of the document you are printing and no matter which format is used to store the original document,
the data must be converted into a PDL data stream or an ASCII text stream with escape codes to be
printed.
Regardless of the PDL or escape-code sequence method used by a printer, its capability to print a rea-
sonable facsimile of what’s on your screen or in your document depends on using the correct PDL or
printer driver for your printer. Failing to switch to the new printer driver when you upgrade to a new
printer will cause your new printer to spit out garbage instead of useful printouts if it uses a PDL dif-
ferent from your old printer.
Printer Control Language
Printer Control Language (PCL) is a page description language developed by Hewlett-Packard for use
in its printers in the early 1980s. As a result of HP’s dominance in the printer market, PCL has become
a standard that is emulated by many other printer manufacturers. Apart from the actual text being