Parallel Port Printers

For many years, the vast majority of printers sold for x86 computers have used the parallel port. As a result, this port is often referred to as the printer port. It should come as no surprise, therefore, that the parallel port is an excellent choice for connecting printers to x86 computers.

The cable used to connect a printer and computer via the parallel port is shown in Figure 20.3. This cable has different types of connectors on its two ends. The connector on the left in Figure 20.3 is a 25-pin male connector that attaches to the computer's parallel port. Printers use an entirely different type of connector—a Centronics connector, shown on the right in Figure 20.3.

The parallel port's speed is very good. This fact, combined with the fact that a parallel port is standard equipment on all modern x86 computers, makes the parallel port an excellent choice for a printer interface. To get the best possible speed, both your computer and your printer must support an advanced parallel-port standard, such as ECP or EPP (see Chapter 16, "Parallel and Serial Ports").


Part IV

Figure 20.3

Printer cables use different connectors on the printer and computer ends.

Figure 20.3

Printer cables use different connectors on the printer and computer ends.

Because most computers come with precisely one parallel port, it's possible to connect precisely one printer to the computer. If you want to connect more than one printer, you have several options:

• Install additional parallel ports Adding a parallel port card enables you to connect two parallel-port printers. The practical limit on parallel ports for x86 computers is three devices, so you might not be able to fulfill all your needs this way if you want to use a Linux computer as a print server for more than three printers.

• Use a switch box A parallel-port switch box lets you connect two or more parallel-port devices to a single parallel port. Switch boxes require manual intervention, though—you need to turn a dial or press a button to direct output to a given printer. This limitation might be acceptable for a desktop computer, but not for a print server.

• Use additional port types There's no law that says you can use only one type of printer interface. You can have a parallel printer and a USB printer connected to a single computer, for instance.

The parallel port is my first choice for a printer interface for use in Linux. There are specific circumstances in which other ports are desirable, though.

Chapter 20

To access a parallel-port printer, you write data to the /dev/lpn device files, where n is a number between 0 and 2. You normally specify the port in the /etc/printcap file, as described later in this chapter.

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