http://www.compphix.com/95
Windows 95/98--BOOT SEQUENCES
The Windows 95 boot sequence is as follows:
When you boot the machine, POST (Power-On Self Test) occurs just as it does for BIOS (Basic Input/Output System) that is not Plug and Play.
The Plug and Play(PnP) BIOS begins by looking at the hardware devices on the system and figuring out which ones are PnP compliant. The BIOS first enables the devices that are not Plug and Play, and then tries to make the PnP devices use the leftover resources.
The Basic Input/Output System looks for devices containing the Operating System (OS) and loads Windows 95, making information about the current allocation of resources available to the OS.
Just as with DOS, the Master Boot Record (MBR) executes the boot record on the hard drive, which looks for the initial hidden files of Windows 95, called IO.SYS.
Again, just as with DOS, IO.SYS loads. If fact, IO.SYS is really a small core DOS module. IO.SYS looks for CONFIG.SYS file, and, if found, the CONFIG.SYS file executes. The CONFIG.SYS file is not required for Windows 95. Many of its functions have been eliminated and incorporated into Windows 95. but you can use the CONFIG.SYS file to load device drivers, if you want. However, the driver loaded in CONFIG.SYS will be a 16 bit driver and it will be slower that the 32 bit drivers that Windows 95 uses.
After CONFIG.SYS is complete, IO.SYS searches for MSDOS.SYS. The role of MSDOS.SYS differs greatly in Windows 95 from that in DOS. In Windows 95, MSDOS.SYS is a hidden file with settings used to customize the boot process.
The functions of the first few entries in MSDOS.SYS look like the following:
WinDir= (Location of the Windows 9x directory)
WinBootDir= (Location of the Windows 9x startup files)
HostWinBootDrv= (Drive that is the Windows boot drive)
BootGUI= (BootGUI=1, automatic graphical startup into Windows 9x is enabled. BootGUI=0, the system boots to a command prompt)
Next, COMMAND.COM loads just as with DOS. COMMAND.COM is used to provide a command interface for users and to execute an AUTOEXEC.BAT file, if it is present.
If AUTOEXEC.BAT is found, it now executes.
The heart of Windows 95 now loads, providing a desktop from which you can execute application software.
WINDOWS 98 BOOT SEQUENCE:
Just as with Windows 95, Windows 98 goes through a boot sequence in the order listed above.
BIOS runs POST
BIOS loads a small DOS core
The DOS core loads Windows 98
Windows 98 has made some some minor changes in what happens during startup, in order to speed up the boot process.
Windows 95 waits 2 seconds, while "Starting Windows 95" is displayed so that you can press a key to alter the boot process.
Windows 98 eliminated the 2 second wait and, in its place, allows you to hold down the CTRL key as it loads. If you do that, you will see the Startup Menu display.
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by: CrazyOnePosted on 2004-02-11 at 01:06:27ID: 10330476
Well what I am posting is for XP but it applies to win2000
The PC Boot Process - Windows XP
http://www.qvctc.commnet.e
Power supply switched on.
The power supply performs a self-test. When all voltages and current levels are acceptable, the supply indicates that the power is stable and sends the Power Good signal to the processor. The time from switch-on to Power Good is usually between .1 and .5 seconds.
The microprocessor timer chip receives the Power Good signal.
With the arrival of the Power Good signal the timer chip stops sending reset signals to the processor allowing the CPU to begin operations.
The CPU starts executing the ROM BIOS code.
The CPU loads the ROM BIOS starting at ROM memory address FFFF:0000 which is only 16 bytes from the top of ROM memory. As such it contains only a JMP (jump) instruction that points to the actual address of the ROM BIOS code.
The ROM BIOS performs a basic test of central hardware to verify basic functionality.
Any errors that occur at this point in the boot process will be reported by means of 'beep-codes' because the video subsystem has not yet been initialized.
The BIOS searches for adapters that may need to load their own ROM BIOS routines.
Video adapters provide the most common source of adapter ROM BIOS. The start-up BIOS routines scan memory addresses C000:0000 through C780:0000 to find video ROM. An error loading any adapter ROM generates an error such as:
XXXX ROM Error
where XXXX represents the segment address of the failed module.
The ROM BIOS checks to see if this is a 'cold-start' or a 'warm-start'
To determine whether this is a warm-start or a cold start the ROM BIOS startup routines check the value of two bytes located at memory location 0000:0472. Any value other than 1234h indicates that this is a cold-start.
If this is a cold-start the ROM BIOS executes a full POST (Power On Self Test). If this is a warm-start the memory test portion of the POST is switched off.
The POST can be broken down into three components:
The Video Test initializes the video adapter, tests the video card and video memory, and displays configuration information or any errors.
The BIOS Identification displays the BIOS version, manufacturer, and date.
The Memory Test tests the memory chips and displays a running sum of installed memory.
Errors the occur during the POST can be classified as either 'fatal' or 'non-fatal'. A non-fatal error will typically display an error message on screen and allow the system to continue the boot process. A fatal error, on the other hand, stops the process of booting the computer and is generally signaled by a series of beep-codes.
The BIOS locates and reads the configuration information stored in CMOS.
CMOS (which stands for Complementary Metal-Oxide Semiconductor) is a small area of memory (64 bytes) which is maintained by the current of a small battery attached to the motherboard. Most importantly for the ROM BIOS startup routines CMOS indicates the order in which drives should be examined for an operating systems - floppy first, CD-Rom first, or fixed disk first.
If the first bootable disk is a fixed disk the BIOS examines the very first sector of the disk for a Master Boot Record (MBR). For a floppy the BIOS looks for a Boot Record in the very first sector.
On a fixed disk the Master Boot Record occupies the very first sector at cylinder 0, head 0, sector 1. It is 512 bytes in size. If this sector is found it is loaded into memory at address 0000:7C00 and tested for a valid signature. A valid signature would be the value 55AAh in the last two bytes. Lacking an MBR or a valid signature the boot process halts with an error message which might read:
NO ROM BASIC - SYSTEM HALTED
A Master Boot Record is made up of two parts - the partition table which describes the layout of the fixed disk and the partition loader code which includes instructions for continuing the boot process.
MBR
With a valid MBR loaded into memory the BIOS transfers control of the boot process to the partition loader code that takes up most of the 512 bytes of the MBR.
The process of installing multiple operating systems on a single PC usually involves replacing the original partition loader code with a Boot Loader program that allows the user to select the specific fixed disk to load in the next step of the process. Windows XP relies on the NTDLR program to provide this same function later in the boot sequence.
Partition Table
The partition loader (or Boot Loader) examines the partition table for a partition marked as active. The partition loader then searches the very first sector of that partition for a Boot Record.
When a partition is formatted with the NTFS file system the first 16 sectors are reserved for the Boot Record (not just 1 sector as in DOS). The additional 15 sectors allow to Boot Record to contain enough program code so that the Boot Loader can locate the XP Master File Table which need not reside in any fixed position on the partition. With the MFT loaded the Boot Loader can locate all of the files that make up the OS.
Operating System
Boot Record
The active partition's boot record is checked for a valid boot signature and if found the boot sector code is executed as a program.
The loading of Windows XP is controlled by the file NTDLR which is a hidden, system file that resides in the root directory of the system partition. NTDLR will load XP in four stages:
1) Initial Boot Loader Phase
2) Operating System selection
3) Hardware Detection
4) Configuration Selection
NTDLR
Initial Phase
During the initial phase NTDLR switches the processor from real-mode to protected mode which places the processor in 32-bit memory mode and turns memory paging on. It then loads the appropriate mini-file system drivers to allow NTDLR to load files from a partition formatted with any of the files systems supported by XP.
Windows XP supports partitions formatted with either the FAT-16, FAT-32, or NTFS file system.
NTDLR
OS Selection
BOOT.INI
If the file BOOT.INI is located in the root directory NTDLR will read it's contents into memory. If BOOT.INI contains entries for more than one operating system NTDLR will stop the boot sequence at this point, display a menu of choices, and wait for a specified period of time for the user to make a selection.
If the file BOOT.INI is not found in the root directory NTDLR will continue the boot sequence and attempt to load XP from the first partition of the first disk, typically C:\.
F8
Assuming that the operating system being loaded is Windows NT, 2000, or XP pressing F8 at this stage of the boot sequence to display various boot options including "Safe Mode" and "Last Known Good Configuration".
After each successful boot sequence XP makes a copy of the current combination of driver and system settings and stores it as the Last Known Good Configuration. This collection of settings can be used to boot the system subsequently if the installation of some new device has caused a boot failure.
NTDLR
Hardware Detection
If the selected operating system is XP, NTDLR will continue the boot process by locating and loading the DOS based NTDETECT.COM program to perform hardware detection.
NTDETECT.COM collects a list of currently installed hardware components and returns this list for later inclusion in the registry under the HKEY_LOCAL_MACHINE\HARDWAR
NTDLR
Configuration Selection
If this computer has more than one defined Hardware Profile the NTDLR program will stop at this point and display the Hardware Profiles/Configuration Recovery menu.
Lacking more than one Hardware Profile NTDLR will skip this step and not display this menu.
Kernel Load
After selecting a hardware configuration (if necessary) NTDLR begins loading the XP kernel (NTOSKRNL.EXE).
During the loading of the kernel (but before it is initialized) NTDLR remains in control of the computer. The screen is cleared and a series of white rectangles progress across the bottom of the screen. NTDLR also loads the Hardware Abstraction Layer (HAL.DLL) at this time which will insulate the kernel from hardware. Both files are located in the <winnt>\system32 directory.
NTDLR
Boot
Device Drivers
NTDLR now loads device drivers that are marked as boot devices. With the loading of these drivers NTDLR relinquishes control of the computer.
Every driver has a registry subkey entry under HKEY_LOCAL_MACHINE
\SYSTEM\Services. Any driver that has a Start value of
SERVICE_BOOT_START is considered a device to start at boot up. A period is printed to the screen for each loaded file (unless the /SOS switch is used in which case file names are printed.
Kernel Initialization
NTOSKRNL goes through two phases in its boot process - phase 0 and phase 1. Phase 0 initializes just enough of the microkernel and Executive subsystems so that basic services required for the completion of initialization become available.. At this point, the system display a graphical screen with a status bar indicating load status.
XP disables interrupts during phase 0 and enables them before phase 1. The HAL is called to prepare the interrupt controller; the Memory Manager, Object Manager, Security Reference Monitor, and Process Manager are initialized.
Phase 1 begins when the HAL is called to prepare the system to accept interrupts from devices. If more than one processor is present the additional processors are initialized at this point. All Executive subsystems are reinitialized 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
I/O Manager
The initialization of I/O Manager begins the process of loading all the systems driver files. Picking up where NTLDR left off, it first finishes the loading of boot devices. Next it assembles a prioritized list of drivers and attempts to load each in turn.
The failure of a driver to load may prompt NT to reboot and try to start the system using the values stored in the Last Known Good Configuration.
SMSS
The last task for phase 1 initialization of the kernel is to launch the Session Manager Subsystem (SMSS). SMSS is responsible for creating the user-mode environment that provides the visible interface to NT.
SMSS runs in user-mode but unlike other user-mode applications SMSS is considered a trusted part of the operating system and is also a native application (it uses only core Executive functions). These two features allow SMSS to start the graphics subsystem and login processes.
win32k.sys
SMSS loads the win32k.sys device driver which implements the Win32 graphics subsystem.
Shortly after win32k.sys starts it switches the screen into graphics mode. The Services Subsystem now starts all services mark as Auto Start. Once all devices and services are started the boot is deemed successful and this configuration is saved as the Last Known Good Configuration.
Logon
The XP boot process is not considered complete until a user has successfully logged onto the system. The process is begun by the WINLOGON.EXE file which is loaded as a service by the kernel and continued by the Local Security Authority (LSASS.EXE) which displays the logon dialog box.
This dialog box appears at approximately the time that the Services Subsystem starts the network service.