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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 system board that must be diagnosed and/or initialized by POST to ensure
system functionality are as follows:
Microprocessor with built-in numeric coprocessor and cache memory subsystem
Direct memory access (DMA) controller (8237 module)
Interrupt system (8259 module)
Three programmable timers (system timer and 8254 module)
ROM subsystem
RAM subsystem
RTC RAM subsystem and real time clock/calendar with battery 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
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