Turn on the power switch.

The power supply performs a self-test. When all the electrical parameters in normal PSU sends the Power Good signal to processor.

The timer of the microprocessor receives a Power Good signal.

With receipt of this signal the timer stops sending Reset signal to the processor, therefore allowing you to join.

CPU begins to execute ROM BIOS code

The CPU loads the ROM BIOS starting at the address FFFF: 0000.

The system performs an initial test of iron.

Every mistake, occurring at this stage is reported defined sound codes (voice), since the video system has not yet initialized.

 The BIOS searches for adapters, that may require you to download their BIOS and.

The most typical case in this case is the video card. Boot procedure scans the pam’Yat from address C000: 0000 for C780: 0000 search for video ROM. Thus loaded system all adapters.

ROM BIOS checks for shutdown or restart.

Procedure two bytes at the address 0000:0472. Any value, 1234h is different from evidence “cold” start.

If the enable ROM BIOS starts the full POST. If it's a reboot, of POST procedure eliminates the memory’for. The POST procedure can be divided into three components:

Video test initializes the video adapter, testing card and video memory’Yat. Identification BIOS shows the version of the firmware, the manufacturer and date. Test pam’verifies memory chips pam’s memory and calculates the size of installed memory’for. Error, which may occur during the POST test can be divided into lethal and not very. In the second case, they are displayed on the screen, but allow to continue the download process. Clear, in the first case, the boot process stops, that is usually accompanied by a series of beep codes.

BIOS reads configuration information from CMOS.

A small area of the pam’for (64 bytes) is powered by a battery on the motherboard. The most important thing to download it - order, which should poll the drives, which one should be first - drive, CD-ROM or hard drive.

If the first is the hard disk drive, The BIOS checks the first sector of the disk for the Master Boot Record. Drive is checked for Boot Record in the first sector.

Master Boot Record - The first sector of the cylinder 0, 0 head, 512 byte size. If it is, it is loaded in pam’Yat, then checked for the correct signature - the last two bytes must be 55AAh. No MBR or these test byte stops the boot process and issues a warning. The MBR itself consists of two parts - the boot loader, program, which gets control at boot from this hard drive; partition table, which contains information about the logical drives, what is on the hard drive.

Operating system

Control is passed to the operating system.

Boot Record is checked for correctness and if the code is correct the boot sector code is executed as a program. Download Windows XP is controlled by the file NTLDR, what is the root directory of the system partition. NTLDR works in four stages:

1.      The initial phase of loading

2.      The choice of the system

3.      Determination of iron

4.      Configure

In the initial phase NTLDR switches the processor into protected mode. Then loads the appropriate file system driver to work with files of any file system, which supports XP.

If the root directory has a BOOT.INI, its contents are loaded into the pam’Yat. If there are entries on more than one operating system, NTLDR will stop - shows the selection menu and waits for input from the user for a certain period of time. If in the process of selection the user has chosen Windows NT, 2000 or XP, we validate press F8 and display the relevant menu with the boot options. After each successful download XP creates a copy of the current combination of driver and system settings known, as Last Known Good Configuration.

If the selected operating system is XP, NTLDR locates and loads the DOS-ovsky program NTDETECT.COM for the determination of iron, installed in the PC’s computer. NTDETECT.COM builds a list of components, which is then used in the HARDWARE key of the HKEY_LOCAL_MACHINE registry branch.

If the PC’s computer has more than one hardware profile, the program stops with the menu selection configuration.

After you select the configuration, NTLDR begins loading the XP kernel (NTOSKRNK.EXE). In the kernel boot process (but before initializing) NTLDR remains Central to the management computer’'yuterom. The screen is cleared and down animation with white rectangles. In addition to the kernel is loaded and Hardware Abstraction Layer (HAL.DLL), so the kernel can abstract from iron. Both files are in the System32 directory.

NTLDR loads the device drivers, marked as bootable. Downloaded NTLDR passes control to the comp’'yuterom on. Each driver has a key in HKEY_LOCAL_MACHINE SYSTEMServices.

NTOSKRNL during the boot process goes through two phases - the so-called phase 0 and phase 1. The first phase initializes only that part of the microkernel and Executive subsystems, need for basic services and continue the download. At this stage the screen displays a graphical screen with a status bar. XP dsabl interruption in the process of phase 0 and includes them only before phase 1. HAL is called to prepare the interrupt controller. Initializes Memory Manager, Object Manager, Security Reference Monitor Process Manager. Phase 1 begins when the HAL is preparing a system for handling device interrupts. If the PC’s computer has more than one processor they started. All Executive subsystems rentalservice in the following order:

1.      Object Manager

2.      Executive

3.      Microkernel

4.      Security Reference Monitor

5.      Memory Manager

6.      Cache Manager

7.      LPCS

8.      I / O Manager

9.      Process Manager

Initializing the input Manager / o starts the download process all system drivers. From the point where stopped drivers NTLDR loaded by priority. A failure in loading the driver can force XP to reboot and try to restore Last Known Good Configuration.

The last task of phase 1 kernel initialization - start Session Manager Subsystem (SMSS). The subsystem is responsible for creating the user environment, that provides the NT interface. SMSS runs in user mode, but unlike other applications SMSS is considered a trusted part of the operating system and “native” the application, that allows her to run the graphics subsystem and login.

SMSS loads win32k.sys - graphics subsystem. The driver switches the comp’computer in graphic mode, SMSS starts all services, which should automatically run at startup. If all devices and services started successfully the download process is deemed successful and creates a Last Known Good Configuration.

The boot process is not considered complete until, until the user login into the system. The process is initialized by the file WINLOGON.EXE, run as a service and supported by the Local Security Authority (LSASS.EXE), which shows the dialog to log in.