A CDE Definition
The commands and functions used to print a job on a network printer. It manages the submission of print jobs by maintaining queues and controlling the transfer of their contents to the printer. It also enables the user to determine the capabilities of the printer and the status of the job and be able to cancel it. It may provide flow control if the underlying transport protocol does not (UDP, IPX, etc.).
A unidirectional protocol such as LPD is mainly responsible for job submission. However, full-featured, bi-directional protocols such as PAP and NDPS include sophisticated printer management, responding to messages and alerts from the printer. The primary printing protocols are the LPR/LPD Unix standard, Apple's PAP, Novell's QMS and NDPS, HP's JetDirect and the Internet's IPP. Contrast with print driver. See page description language.
page description language
A high-level language for describing the layout of a page to be displayed or printed. The two major languages are Adobe's PostScript and HP's PCL, which are device independent and built into most printers. Adobe's PDF format is also widely used for printing as well as publishing on the Web (see PostScript, PCL and PDF). The standard for page-oriented XML documents is XSL-FO (see XSL).
It's Done in the Printer
With regard to PostScript and PCL, much of the character and graphics shaping is done within the printer rather than in the user's computer. Instead of downloading an entire font (containing the design of each and every character) from the computer to the printer, a command to build a particular font is typically sent, and the printer creates the characters from font outlines.
Likewise, in a similar way, a command to draw a circle is sent to the printer rather than sending the actual bits of the circle image. However, bitmaps can also be used when necessary.
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