Windows NT Local Client

Windows-based applications and MS-DOS-based applications print in different ways and follow different rules. Windows-based applications send print jobs to printers added in the Printers folder. They typically use the printer drivers associated with those printers. However, some high-end desktop publishing or CAD applications have their own internal program copy of printer drivers.

In contrast, MS-DOS-based applications are unaware of the printers added in the Printers folder. They print to ports instead of to printers. This can cause problems. Whereas you could add several dozen printers in the Printers folder, most MS-DOS-based applications are limited to ports like LPT1–LPT3 and COM1–COM2. Windows NT accommodates MS-DOS-based applications in the following ways:

• If the port is controlled by the network redirector (for example, when a net use command redirects output to a shared resource), the redirector determines where the job goes.

• If the port is not controlled by a network redirector, but a printer prints to that port, the job is submitted to that printer, and that printer's spooling options take effect.

• If the port is not controlled by a network redirector, and no printer prints to that port, the job goes directly to the port device driver and prints (presuming, of course, that a print device is connected to that port).

EXAMPLE

Assume you are interactively logged on to a print server, and that there are two printers in the Printers folder and two print devices. The server is named \\PSERVER1, the printer named HPV prints to an LPT2 port supplied by a separate IO card, and the printer named HPIIISI prints to the FILE port. Both HPV and HPIIISI are shared on PSERVER1 over the network. There are print devices connected to both LPT1 and LPT2. You open a command prompt and type the following command:

NET USE LPT3: \\PSERVER1\HPIIISI. 

When you copy a file to each of LPT1, LPT2, and LPT3, the following results:

COPY TEST.TXT LPT1:

NTVDM checks with the redirector and finds that the redirector is not managing LPT1. It checks with the spooler and finds that neither of the defined printers prints to LPT1, so the job goes to the parallel port device driver.

COPY TEST.TXT LPT2:

NTVDM checks with the redirector and finds that the redirector is not managing LPT2. It finds that the printer HPV is printing to LPT2. NTVDM submits the job to HPV and that printer's spooling options take effect as the job is printed on LPT2.

COPY TEST.TXT LPT3:

NTVDM checks with the redirector and finds that the redirector is managing LPT3, so the redirector takes control. The redirector is set so that data sent to LPT3 is actually sent to the print share \\PSERVER1\HPIIISI. It sends the job to that share and once it arrives, HPIIISI's spooling options take effect. Although you usually use the net use command to assign a local port to a remote shared resource, it is perfectly legal to assign a local port to a local shared resource. This is often useful in testing and troubleshooting.