57 Chapter 4Power-On Self-Test (POST)Each time you turn on the system, the Power-on Self Test (POST) is initiated. Several items are tested duringPOST, but is for the most part transparent to the user.The Power-On Self Test (POST) is a BIOS procedure that boots the system, initializes and diagnoses thesystem components, and controls the operation of the power-on password option. If POST discovers errors insystem operations at power-on, it displays error messages on screen, generates a check point code at port80h or even halts the system if the error is fatal.The main components on the main board that must be diagnosed and/or initialized by POST to ensure systemfunctionality are as follows:T Microprocessor with built-in numeric co-processor and cache memory subsystemT Direct Memory Access (DMA) controllerT Interrupt systemT Three programmable timersT ROM subsystemT RAM subsystemT RTC RAM subsystem and real time clock/calendar with battery backupT Onboard serial interface controllerT Onboard parallel interface controllerT Embedded hard disk interface and one diskette drive interfaceT Keyboard and auxiliary device controllersT I/O portsT PS/2-compatible mouse portT PS/2-compatible keyboard portT Serial portsT Parallel portsT USB port
