Printer Drivers

Printer drivers are the software that enables an application to communicate with the variety of available print devices, regardless of the device type, model, or programming language interpreter.

In general, printer drivers are composed of three files that work together as a printer-driver unit:

• A printer graphics driver. This file renders device driver interface (DDI) commands from the graphics engine to commands that a print device can understand. Each graphics driver renders a different printer language. For example, a Pscript.dll renders PostScript printer language.
• A printer interface driver. This file provides the user interface you see when you configure a printer.
• A characterization data file. This file provides information about the configuration capabilities of a specific make and model of print device, including what resolutions it is capable of, whether it can print on both sides of the page, and what paper sizes it can accept.

These three files work as a unit. For example, when you set up and configure a new printer, the interface driver queries the characterization data file and then displays the available choices. Then, when you print, the graphics driver queries the interface driver about your selections so that it can create the proper printer commands.

Printer drivers are generally not binary-compatible across hardware-processor platforms. Consequently, printer drivers must be installed on the Windows NT print server for each Windows NT client hardware platform. For example, when x86-based clients running Windows NT Workstation are served for printing by a Alpha AXP-based Windows NT Server, you must install printer drivers on the Alpha AXP-based print server.

The Windows NT and Windows 95 print client first attempts to use a local printer driver. If none is available, the Windows NT print server downloads the printer driver to the client computer's hard disk. The client application then uses its copy to create the print job.

In previous versions of Windows NT, printer drivers ran in user mode. With Windows NT 4.0, printer drivers run in kernel mode, thus reducing memory requirements and improving performance. For more information about user and kernel modes, see Chapter MESMegan E. Sheppard5 "Windows NT Workstation Architecture," in the Windows NT Workstation Resource Guide.

Note Print clients running Windows NT 4.0 won't be able to use printer drivers downloaded from a print server running an earlier version of Windows  NT. You'll need to make sure that the client computer has the 4.0 printer drivers, or better yet, use 4.0 on your print servers. A print server running Windows NT 4.0 can supply earlier version printer drivers to downlevel Windows print clients, if necessary.

Platform-specific printer drivers are available for the following:

• Intel x86-based computers running Windows NT 4.0, 3.5, or 3.51 and Windows 95
• MIPS RISC-based computers running Windows NT 4.0, 3.5, or 3.51 and Windows 95
• Digital Alpha AXP-based computers running Windows NT 4.0, 3.5, or 3.51 and Windows 95
• IBM PowerPC running Windows NT 4.0, or 3.51 and Windows 95

Print devices can be classified as one of three types: raster, PostScript, or plotter. To support these three classes of print devices, Windows NT provides the following generic printer drivers:

• Universal printer driver
• PostScript printer driver
• HP-GL/2 plotter driver