post4dPCI POST Code Display POST4D During the Power On Self-Test (POST), most PC BIOS write diagnostic codes to port 80h or 84 (jumper selection). Use POST4D to display these codes onby Add Komoncharoensiri, Director of Technical Services at 4D Inc. Here we go with another set of tips and tricks. The 4D Knowledge Base is a library of information about 4D technology where weekly tech tips and monthly