Download POST

Computer
Startup Sequence
Overview
Richard Goldman
© February 28, 2001
Power
Supply
The computer
is connected to
110 Volt AC
power from
the wall outlet.
(C) Richard L. Goldman
2
Power
Supply
Ground
+5 VDC
-5VDC
+12VDC
-12VDC
+3.3VDC
When the computer is turned
on the power supply converts
power from the wall outlet to
DC voltages that the computer
can use.
(C) Richard L. Goldman
3
Power
Supply
System
Board
CPU
After the power supply is
stable and it has completed a self
test – the power supply changes
the voltage on the Power Good
(PG) line from 0 to 5 volts.
This allows the CPU to stop
resetting and begin operation.
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4
Power
Supply
System
Board
CPU
Chip Set
Sys. BIOS
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The first thing that the CPU
does is to locate and run
POST program located in
the System ROM BIOS.
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Power
Supply
The POST
program
initially
locates and
tests the basic
functionality
of the central
hardware.
System
Board
CPU
Chip Set
Sys. BIOS
CMOS RAM Battery
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6
Power
Supply
System
Board
Chip Set
CPU
If any errors are
found during
this test - Beep
Codes are
sounded and the
boot process is
stopped.
Sys. BIOS
CMOS RAM Battery
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Power
Supply
System
Board
CPU
Monitor
Sys. BIOS
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The next task is to
Chip Set locate the Video ROM
BIOS.
Once located the
Video ROM BIOS is
CMOS RAM
Battery
tested
and executed
providing a video display.
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Power
Supply
System
Board
CPU
Monitor
Chip Set
Keyboard
Hard
Drive
Floppy
Drive
Sys. BIOS
Printer
(C) Richard L. Goldman
Then a search for any
CMOS
RAM Battery
additional
BIOS’s is conducted.
Any additional BIOS’s found
are tested and executed.
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Power
Supply
System
Board
Memory
CPU
Monitor
Chip Set
Keyboard
The next item checkedHard
is the System Memory. Drive
Floppy
Drive
Sys. BIOS
Printer
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CMOS RAM Battery
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Power
Supply
System
Board
Memory
CPU
Monitor
Chip Set
Keyboard
Sys. BIOS
Printer
(C) Richard L. Goldman
Hard
Drive
Floppy
Drive
The last command that the
System BIOS runs is the Bootstrap
Loader.
CMOS
RAM Battery
The Bootstrap Loader locates and
passes control to the Master Boot
Record.
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Power
Supply
System
Board
Memory
CPU
OS
Monitor
Chip Set
Keyboard
Sys. BIOS
Printer
(C) Richard L. Goldman
Hard
Drive
Floppy
Drive
The Master Boot Record locates
the Operating System and loads it
into Memory
CMOS
RAM Battery
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