Port drivers are dynamic link libraries (DLLs) that contain a set of 32-bit functions, which provide helper functions for the spooler and Workplace Shell. For each port driver DLL, there should be a physical port driver (SYS file) installed in the CONFIG.SYS file. The file type of a port driver is .PDR.
The operating system, by default, provides two port drivers; SERIAL.PDR supports COM1 - 4, and PARALLEL.PDR supports LPT1 - 3. For any other port, the supplier of the physical port software is responsible for providing a Presentation Manager port driver if it is necessary.
The functions exported from a port driver are: