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72 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:
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Microprocessor with built-in numeric co-processor and cache memory subsystem
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Direct Memory Access (DMA) controller
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Interrupt system
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Three programmable timers
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ROM subsystem
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RAM subsystem
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RTC RAM subsystem and real time clock/calendar with battery backup
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Onboard serial interface controller
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Onboard parallel interface controller
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Embedded hard disk interface and one diskette drive interface
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Keyboard and auxiliary device controllers
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I/O ports
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PS/2-compatible mouse port
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PS/2-compatible keyboard port
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Serial ports
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Parallel ports
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USB port