The PC Boot Process (in detail)
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
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.
Date/time, drive configuration, port configuration, default
interrupts for PCI bus and integrated peripherals, if any.
Extended video ROM loaded into upper memory
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 GUIWindows NT4/2000 boot files
NTDETECT.COM
NTLODR
BOOT.INI
[BOOTSECT.DOS]
[AUTOEXEC.BAT] =====>