Specifications

Both PCL and PostScript are available in a variety of printers. The Macintosh printing platform is
designed around PostScript, which is standard equipment in all Apple’s laser printers. Obviously,
because Hewlett-Packard developed the PCL standard, all their printers use that PDL by default.
However, most of the HP laser printers are available in a version with PostScript as well. In addition,
most HP laser printers can accept a special add-on module that provides the printer with PostScript
support. Very few inkjet printer models contain a PostScript interpreter, and those few are normally
B-size (11”×17” paper) or larger units designed for graphic-arts prepress work.
Note
Different HP printers use different levels of PCL. You also should know that printers that nominally use the same level of PCL
might vary in their implementations of PCL commands. Search HP’s Web site for details about an HP printer model’s use of
PCL.
Many other manufacturers also use PCL or PostScript (or both), which they have either licensed from
HP or Adobe or emulated themselves for their printers. The question of whether a printer has gen-
uine, licensed versions of its PDLs can be very important. Numerous instances have occurred through-
out the history of these PDLs in which unauthorized or poorly emulated versions of PCL and
PostScript have been foisted on the public as the real thing. In the mid-1980s, the term “LaserJet Plus
Emulation” came to have as little meaning as “Hayes compatible” did for modems. Nowadays, most
of the PCL (usually version 5) emulations used in other manufacturers’ printers are quite good, but
PostScript is a far more complex language and is more difficult to emulate. You still can find discrep-
ancies between an emulated version of a PDL and the real thing that result in visible differences in
the printed output.
Here again, the PDL emulation issue largely depends on your interactions with other users. If you
have a printer with an emulated version of PostScript and a printer driver that accurately addresses
that emulated printer firmware, it matters little if the language does not conform precisely to the
Adobe specifications. If you are sending your PostScript output to a service bureau for printing on an
image setter, however, the discrepancies between an emulated PostScript and the real thing can make
a vast difference.
Whenever possible, you should purchase a printer that uses the genuine PDL licensed from its creator.
A minimum of PCL 5 or PostScript Level 2 is preferable.
Many laser printers support both PCL and PostScript, and you should check to see how a printer han-
dles mixed jobs using various PDLs. The best printers detect the PDL of each job as it arrives in the
printer and automatically switch to the appropriate language. If a printer does not have this feature,
you might have to send a command with each print job triggering the mode change. For a single user
on a standalone system, this is not much of a problem. For a printer connected to a network, know-
ing for sure the order in which jobs are printed is often difficult unless someone constantly monitors
the print queue. In addition, manual mode changes can be difficult to organize.
Escape Codes
Virtually all laser printers and most inkjet printers support at least one page description language, but
some printers (especially dot-matrix) do not, and in this case the printer driver usually communicates
with the printer using escape code sequences. Similar to the PCL commands described earlier, escape
codes are control sequences used to activate the features of a particular printer. Escape codes are so
named because the ASCII value for the Esc key (decimal 027) is used as the first character of the code
to signal to the printer that what follows is an instruction code and not a textual element of the doc-
ument being printed.