Hardware Boot Process
Step 1: You push the power button
Step 2: The power supply perfroms a self-test (known as the POST). When all voltages and current levels are acceptable, the supply indicates that the power is stable and sends the Power_Good signal to the motherboard. The time from the switch-on to the Power_Good is normally between .1 to .5 seconds.
Step 3: The microprocessor timer chip recieves Power_Good signal, which causes it to stop generating a reset signal to the microprocessor.
Step 4: The microprocessor begins executing the ROM BIOS code, starting at the memory address FFFF:0000. Because this location is only 16 bytes from the very end of the available ROM space, it contains a JMP (jump) instruction to the actual ROM BIOS starting address.
Step 5: The ROM BIOS perfroms a test of the central hardware to verify basic system functionality. Any errors that occur are indicated by a series of "beep" codes because the video system has not been initialized.
Step 6: The BIOS performs a video ROM scan of memory locations C000:0000-C780:0000 looking for video adapter ROM BIOS programs contained on the video adapter found either on the card plugged into a slot or integrated onto the motherboard. If scan locates a video ROM BIOS, it is tested by a checksum procedure.
Step 7: The motherboard ROM BIOS scan memory locations C800:0000-DF80:0000 in 2KB increments for any other ROMs located on any other adapter cards.
Step 8: The ROM BIOS checks the world value at memory location 0000:0472 to see whether this start is a cold start or warm start. If it is a cold start the full POST executes, if its a warm start, a mini-POST executes.
Step 9: The ROM BIOS searches for a boot record at cylinder 0, head 0, sector 1 (the very first sector) on the default boot drive. Sucessful completion of POST is indicated by a beep.
Step 10: If no boot record can be read from drive A: the BIOS then looks for a master book record at cylinder 0, head 0, sector 1 (the very first sector) of the first hard disc. If this sector is found, it is loaded into memory address 0000:7C00 and tested for signature.
Step 11: The MBR searches its built-in patition table for entries for a boot indiator byte parking an active partition entry.
If an active partition is found in the MBR, the partition boot record from the active partition is loaded and tested.
Software boot process: (Microsoft Windows XP)
Step 12: The partition boot sector loads Ntldr (NT Loader). It then switches the processor to protected mode and starts the file system, and reads the contents of Boot.ini.
Step 13:Ntdetect.com gathers hardware configuration data and passes this infromation to Ntldr.
Step 14: The kernel loads. Ntldr passes infromation collected by Ntdetect.com to Ntoskrnl.exe. Ntoskrnl.exe then loads the kernal.
Step 15: Drivers load (You see the Windows XP loading screen)
Step 16: User signs on
Step 17: The boot process is complete and the system is ready for the next set of instructions.