72 Chapter 4
Power-On Self-Test (POST)Each time you turn on the system, the Power-on Self T e st ( POST) is ini tia ted. Sever al ite ms are test ed 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 operat ion of the power - on passwor d optio n. If POST disco ver s error s 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 initializ ed by POST to ensure syst em
functionality are as follows:
!Microprocessor with built-in numeric co-proce ssor and cache memory subsystem
!Direct Memory Access (DMA) controller
!Interrupt system
!Three programmable timers
!ROM subsystem
!RAM subsystem
!RTC RAM subsystem and real time clock/calendar with batte ry backup
!Onboard serial interface controller
!Onboard parallel interface controller
!Embedded hard disk interface and one diskette drive interface
!Keyboard and auxiliary device controllers
!I/O ports
! PS/2-compatible mouse port
! PS/2-compatible keyboard port
!Serial ports
!Parallel ports
!USB port