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62 Chapter 4
Power-On Self-Test (POST)
Each time you turn on the system, the Power-on Self Test (POST) is initiated. Several items are tested during
POST, 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 the
system components, and controls the operation of the power-on password option. If POST discovers errors in
system operations at power-on, it displays error messages on screen, generates a check point code at port
80h 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 system
functionality are as follows:
T Microprocessor with built-in numeric co-processor and cache memory subsystem
T Direct Memory Access (DMA) controller
T Interrupt system
T Three programmable timers
T ROM subsystem
T RAM subsystem
T RTC RAM subsystem and real time clock/calendar with battery backup
T Onboard serial interface controller
T Onboard parallel interface controller
T Embedded hard disk interface and one diskette drive interface
T Keyboard and auxiliary device controllers
T I/O ports
T PS/2-compatible mouse port
T PS/2-compatible keyboard port
T Serial ports
T Parallel ports
T USB port