Spool files are files used by the Windows® operating system that speak to the printer and give it specific instructions on how to print a file or document. Spool files come in two varieties: enhanced metafile (EMF) and raw. The difference is in how the printer processes the spool file. Raw spool files have advantages, such as causing fewer technical problems than EMF, and disadvantages, such as a lower print quality and taking longer to print, depending on the situation.
The general role of a print spool file is to act as an inbox and outbox for commands that deal with the printer. The inbox would be the user pulling up a document and commanding the computer to print out the document. This activates the spool file, which takes the command into the inbox and then begins speaking with the printer. The outbox portion activates when the printer prints, according to the directions of the spool file.
Spool files come either as EMF or raw. EMF spool files are processed through the printer and are considered device-independent, which means a document’s resolution is unchanged despite the document's dots per inch (DPI). Raw files are not processed through the printer; the printer just sees the print instructions are plain text. Raw spool files speak with PostScript®, a common language found in most printers.
Raw spool files have an advantage over EMF spool files because they are seen as plain text. That means, if the printer cannot understand the EMF, using raw spool files may correct the error. These files speak with PostScript® instead of the printer itself, which allows the files to create some effects that EMF would not be able to create and to perform some commands that are impossible for EMF files. EMF files can commonly be changed to raw, or used as raw files, just by altering the printer’s preferences.
The disadvantages of raw spool files include its occasionally lower printer quality and speed. Unlike EMF files, raw spool ones are device-dependent, so the resolution may be lower, especially for images printed from the Internet. This problem will generally not occur with text documents and graphic files made in a graphic design program. On another level, if the printer does not include PostScript®, then a raw spool file will not work. They also tend to print more slowly than the EMF variety.