The PC Boot Process (in detail)
    1. Power-On Self Test (POST)

      2. ROM BIOS checks functionality/presence of: CPU, memory, keyboard, video adapter, floppy/hard disk

      Also performs internal self-check called checksum

      CPU registers are cleared/reset

      Checks for Warm/Cold power-on status

      Warm (soft boot) activated by CTRL+ALT+DEL, memory tests skipped

      Cold boot is from OFF power to ON power.

      First 16K of memory checked

       

    2. System Initialization

      3. Supplementary controller chips on motherboard are activated.

      Values in System BIOS are moved into RAM

      Interrupt controller is set up

      Interrupt vector table loaded into memory (from 00000h to 003FFh

      (Interrupt controller constantly monitors CPU for specific signals called interrupts,
      which activate specific service routines for I/O, and video. Most interrupts can be
      masked (disregarded) when system performs read/write diagnostic tests. NMI
      (non-maskable interrupts) can't be regarded. NMIs used to respond to critical system
      errors to halt processing.

    3. CMOS configuration values read and loaded.

      4. Date/time, drive configuration, port configuration, default
      interrupts for PCI bus and integrated peripherals, if any.
      Extended video ROM loaded into upper memory

    4. BIOS extensions for Bus peripherals loaded (SCSI controller or
      network card/sound card)

Tip: if machine won't boot, look for CMOS and operating system options to restore the default settings

POST tests have beep codes and error messages to inform you when the boot process is unsuccessful. The manual for the motherboard may be necessary to decode them.

Review Boot Process

MS DOS/ Windows 9.x boot files

IO.SYS
MSDOS.SYS
[CONFIG.SYS]
COMMAND.COM
[ AUTOEXEC.BAT] =====> WIN.COM loads GUI

Windows NT4/2000 boot files

NTDETECT.COM
NTLODR
BOOT.INI
[BOOTSECT.DOS]
[AUTOEXEC.BAT] =====>