Print job

The print spooler organizes print requests from clients by creating a queue of print jobs. Each print job is destined for a particular printer. A print job may be spooled (written to a file on disk and printed later) or printed directly to the printer.

Printer spool files

Print jobs that are not printed directly are stored in spool files on disk. Two types of spool file formats are supported by the default Windows 95 spooler: the enhanced metafile (EMF) format, which is device-independent, and raw format, which is device dependent.

Enhanced metafile spool files

Enhanced metafiles (EMFs) are one type of spool file used by the default Windows 95 print spooler (raw files are the other type). EMFs are also the native graphics file format for Windows 95. EMF spool files are used to greatly reduce the amount of time between the time the application user initiates a print request and when control is returned back to the operating system. This is done by storing only the GDI function calls that produce the graphics object the application wants printed, allowing the much more time-consuming execution of the function calls to be carried out later, in the background, when the spool file is "played back." The way EMF spool files are encoded also provides the advantage of printer device-independence. In other words, a picture measuring 2 inches by 4 inches on a VGA display and stored in an EMF maintains those original dimensions when it is printed on a 300 dpi laser printer or a 75 dpi dot matrix printer.

Raw spool files

Raw spool files are device-dependent. The spooled data is destined and formatted for a particular device and does not need to be printable on a different device. An example of a raw spool file is an encapsulated PostScript file, which is formatted to be understood by the PostScript printer for which it is destined, but which is just raw data to the Windows 95 spooler.

Port

The physical hardware through which a printer connects to the computer.

Bi-directional printer

A printer that supports two-way communication between the printer and code running on the computer to which the printer is connected. This two-way communication is used for two primary purposes: printer configuration and monitoring device status. An example of a bi-directional printer is an HP LaserJet 4Si.