A simulated printer. If a program is ready to print, but all printers are busy, the printing subsystem in the operating system transfers the printer output to disk and keeps it there until a printer becomes available. See print spooler. Another use of a virtual printer is to analyze printer output before printing it. For example, if printer output is sent to a virtual printer from GreenPrint Technologies (www.printgreener.com) instead of the real printer, GreenPrint ensures that the last page does not print blank or with only a couple lines. It can also be used to preview the document and delete unwanted pages.