GDI on Windows, PostScript on UNIX
Network printing is one of the most complicated and error-prone
day-to-day tasks any user or administrator may encounter. This is
true for all OS platforms, and there are reasons it is so.
You can't expect to throw just any file format at a printer and have it get printed. A file format conversion
must take place. The problem is that there is no common standard for print file formats across all
manufacturers and printer types. While PostScript (trademark held by Adobe) and, to an extent, PCL (trademark
held by Hewlett-Packard) have developed into semi-official “standards” by being the most widely
used page description languages (PDLs), there are still many manufacturers who “roll their own”
(their reasons may be unacceptable license fees for using printer-embedded PostScript interpreters, and so on).