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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. (C) Richard L. Goldman 4 Power Supply System Board CPU Chip Set Sys. BIOS (C) Richard L. Goldman The first thing that the CPU does is to locate and run POST program located in the System ROM BIOS. 5 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 (C) Richard L. Goldman 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 (C) Richard L. Goldman 7 Power Supply System Board CPU Monitor Sys. BIOS (C) Richard L. Goldman 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. 8 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. 9 Power Supply System Board Memory CPU Monitor Chip Set Keyboard The next item checkedHard is the System Memory. Drive Floppy Drive Sys. BIOS Printer (C) Richard L. Goldman CMOS RAM Battery 10 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. 11 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 12