A device definition consists of the logical name of a device such as LASER_PRINTER or SCANNER, and the commands DP4 needs to communicate with the device.
You set up a device definition using the DP4 utility DFSETUP.
DP4 gives you two levels of definition for output devices:
At this level, you define the set of parameters that relate to the device. For example, for a laser printer, you might define the printer commands to change the paper orientation and the font. A device group can in fact refer to a whole collection of devices, defined as Component Output Devices (CODs).
A DP4 application accesses a device using what is, perhaps unfortunately, known as a POD, which stands for parameterised output device. This is best though of, and used, as a "logical device". A POD selects a specific combination of device group and parameters that you want to use for a particular task. For example a system might be set up different PODs for differing types of reports (e.g. Sales Reports, or Management Reports), and you might set these to use the same or different actual printers depending on the actual installation . A POD can be reconfigured to use a completely different device without the application being affected in any way.
The input device definition lets you specify multiple input devices. This means that more than one input device may be active at any one time in an application. For example, a POS terminal can have both a keyboard and a scanner attached. The cashier is free to use either or both devices for the input of a product code. Most DP4 systems use the same definitions for input devices