1. Computer Startup Sequence Overview
Richard Goldman
© February 28, 2001

2. The computer is connected to 110 Volt AC power from the wall outlet.
Supply
The computer is connected to 110 Volt AC power from the wall outlet.
(C) Richard L. Goldman

3. 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

4. This allows the CPU to stop resetting and begin operation.
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.
(C) Richard L. Goldman

5. Boot Sequence Overview
April 21, 2017
Power
Supply
System
Board
CPU
Chip Set
System ROM address is always located at FFFF:0000.
The first thing that the CPU does is to locate and run POST program located in the System ROM BIOS.
Sys. BIOS
(C) Richard L. Goldman
(C) Richard L. Goldman

6. Boot Sequence Overview
April 21, 2017
Power
Supply
System
Board
CPU
The POST program initially locates and tests the basic functionality of the central hardware.
Chip Set
Sys. BIOS
CMOS RAM
Battery
(C) Richard L. Goldman
(C) Richard L. Goldman

7. System Power Board Supply CPU
If any errors are found during this test - Beep Codes are sounded and the boot process is stopped.
Chip Set
Sys. BIOS
CMOS RAM
Battery
(C) Richard L. Goldman

8. The next task is to locate the Video ROM BIOS.
Power
Supply
System
Board
CPU
Monitor
Chip Set
The next task is to locate the Video ROM BIOS.
Once located the Video ROM BIOS is tested and executed providing a video display.
Sys. BIOS
CMOS RAM
Battery
(C) Richard L. Goldman

9. Then a search for any additional BIOS’s is conducted.
Power
Supply
System
Board
CPU
Monitor
Hard
Drive
Chip Set
Keyboard
Floppy
Drive
Printer
Sys. BIOS
Then a search for any additional BIOS’s is conducted.
Any additional BIOS’s found are tested and executed.
CMOS RAM
Battery
(C) Richard L. Goldman

10. The next item checked is the System Memory. Chip Set
Power
Supply
System
Board
CPU
Memory
Monitor
Hard
Drive
The next item checked is the System Memory.
Chip Set
Keyboard
Floppy
Drive
Printer
Sys. BIOS
CMOS RAM
Battery
(C) Richard L. Goldman

11. The last command that the System BIOS runs is the Bootstrap Loader.
Power
Supply
System
Board
CPU
Memory
Monitor
Hard
Drive
Chip Set
Keyboard
Floppy
Drive
Printer
The last command that the System BIOS runs is the Bootstrap Loader.
The Bootstrap Loader locates and passes control to the Master Boot Record.
Sys. BIOS
CMOS RAM
Battery
(C) Richard L. Goldman

12. OS System Power Board Memory Supply CPU Hard Drive Chip Set Floppy
Monitor
Hard
Drive
Chip Set
Keyboard
Floppy
Drive
Printer
The Master Boot Record locates the Operating System and loads it into Memory
Sys. BIOS
CMOS RAM
Battery
(C) Richard L. Goldman