In the Windows environment, some devices/ports have specific names, such as PRN, COM1, COM2, LPT1, LPT2, and CON. The device/port names resemble files in that they can be opened, read from, written to, and closed. Entering the names of these devices/ports in APDL, however, causes unpredictable behavior, including system freezes or fatal error conditions. Therefore, do not issue PC device/port names as commands.