Sim-Ex™ Tutorial for A+ : Operating Systems

2. Installation, Configuration, and Upgrading

2.3 Identify the basic system boot sequences and boot methods, including the steps to create an emergency boot disk with utilities installed for Windows 9x/Me, Windows NT 4.0 Workstation, Windows 2000 Professional, and Windows XP.

Boot Sequence


The computer runs the Power On Self Test (POST) which checks BIOS, CPU, RAM, Video, Keyboard, drives, etc. Once POST is completed, the next step is to load the Operating System (OS). The minimum information required on the hard drive is called the Master Boot Program that is needed to locate the beginning of the OS on the drive. The order in which the files are required is given below:

POST--> OS --> MBR--> Partition Table--> DOS Boot Record (IO.SYS)--> MSDOS.SYS --> COMMAND.COM.

The entire process of DOS boot is described below:

  • BIOS locates the Master Boot Record (MBR) on the hard drive.
  • The partition table find the physical location of the logical boot drive and turns to the boot record of that logical drive
  • The boot record (a very short program) loads two hidden files into memory. These files are IO.SYS and MSDOS.SYS
  • Once these two files are loaded, the boot record program is longer needed and turns control over to a file stored on MSDOS.SYS
  • This program looks on the hard drive for a file named CONFIG.SYS. This file contains commands that tell DOS how many files it can open at any one time (FILE=) and how many file buffers (a temporary holding area for a file) to create (BUFFERS=), etc.
  • When CONFIG.SYS is done, MSDOS loads COMMAND.COM
  • AUTOEXEC.BAT (Automatically Executed Batch file) holds a list of DOS commands that are automatically executed each time DOS loads. Few of these commands are:
    • PROMPT $P$G this instructs DOS to display the current directory name and the current drive name as part of the prompt.
    • PATH Tells DOS where to look for program files. Example: C:Windows.
    • AUTOEXEC.BAT also loads TSRs (terminate and stay resident programs).
  • The boot process is completed after AUTOEXEC.BAT has finished executing. At this point, COMMAND.COM takes control and you have the command Prompt (C:>).

Windows 95/98 Boot Sequence:

The Windows 95 boot sequence is as follows:

  • When you power-on 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. The BIOS first enables the devices that are not Plug and Play, and then tries to make the PnP devices use the remaining resources.
  • The BIOS 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. 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.
  • 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.
  • Once the OS loads completely, a desktop GUI appears, from which you can browse, run commands, or applications.

WINDOWS 98 Boot Sequence:

Windows 98 boot process is very similar to Windows 95.

  • BIOS runs POST
  • BIOS loads a small DOS core
  • The DOS core loads Windows 98

To speed up boot process, the 2 second wait cycle of Windows 95 while "Starting Windows 95" has been replaced with a hold down CTRL key. You just need to hold down the CTRL key in Windows 98 to go to Startup Menu display.

Windows XP Boot Sequence:

As with other Windows Operating Systems, when you turn on your PC, it goes through an elaborate boot up process. It begins when the computer performs the POST (Power-On Self Test), followed by the POST. The BIOS then reads the MBR (Master Boot Record) which is in the first sector of the first hard disk and transfers control to the code in the MBR which was created during the XP Setup. This is where Windows takes over the startup process.

  • The MBR reads the boot sector which is the first sector of the active partition. This sector contains the code that starts Ntldr which is the boot strap loader for Windows XP. The first role of Ntldr is to allow full memory addressing, start the file system, read boot.ini and put up the boot menu. IMPORTANT: Ntldr must be located in root folder of the active partition along with, boot.ini, bootsect.dos (for dual booting) and Ntbootdd.sys (needed with some SCSI adapters).
  • Selecting XP from the boot menu (in case of multiple boot options) causes Ntldr to run to get information about installed hardware. Ntldr then uses the ARC path specified in the boot.ini to find the boot partition, where Windows XP is installed. Ntldr loads the two files Ntoskrnl.exe and Hal.dll. These files must be located in the %SystemRoot%System32 folder.
  • Ntldr reads the registry files, selects a hardware profile, control set and loads device drivers, in that order.
  • Then, Ntoskrnl.exe takes over and starts Winlogon.exe which starts Lsass.exe (Local Security Administration), This program displays the Welcome screen and allows the user to log on with his/her user name and password.

Alternative Boot Methods

Using a Startup disk

A startup disk is useful in case you have a problem booting up the computer. You can boot the computer from a startup disk and try to fix what is actually causing the boot problem. The startup disk is created during the operating system installation. You can also create it at a later point, after the installation of the Operating System. Important files that are needed for booting the computer are stored in the startup disk. The list of files that are stored in the Startup disk may differ for various Operating Systems as below:.

Windows 95:

The files copied on to the Windows 95 Startup Disk include the following:

  • attrib.exe - a file attribute utility
  • - a Core operating system file
  • drvspace.bin - disk compression utility
  • ebd.sys- Utility for the startup disk
  • - a text editor
  • fdisk.exe - disk partition utility
  • - disk format utility
  • io.sys - core operating system file
  • msdos.sys - core operating system file
  • regedit.exe - real-mode Registry Editor
  • scandisk.exe - disk status and repair utility
  • scandisk.ini - disk status utility configuration file
  • - system transfer utility

Windows 98:

The following files are added to the Windows 98 Startup Disk:

  • Startup Menu
  • Real-Mode IDE CD-ROM support
  • Real-Mode SCSI CD-ROM support
  • file ( These are Cabinet files containing extract utilities)
  • RAMDrive
  • New extract command: Ext.exe

Utilities contained in the file include the following:

  • Attrib.exe - file attributes utility
  • Chkdsk.exe - disk check tool
  • Debug.exe - debug utility.
  • - a text editor.
  • Ext.exe - file extract utility.
  • - disk format utility, use with care.
  • Help.txt - Useful for troubleshooting purpose, a help document
  • Mscdex.exe - CD-ROM file extension for MS-DOS.
  • - restart your computer.
  • Scandisk.exe - disk scan tool.
  • Scandisk.ini - disk scan configuration file.
  • - system transfer tool.
  • Uninstal.exe - tool for removing Windows 98.

A start-up disk may be created during installation of the OS or at a later stage. To create a Startup disk at a later stage, use Add/Remove Programs, and select Start Disk stab in Windows 9x.

Windows 2000:

  • Insert disk into the floppy disk drive
  • Insert the Windows 2000 CD-ROM
  • Browse to bootdisk folder of the CD-ROM drive
  • Double click makeboot.exe, and follow the instructions on screen.

You can also create an Emergency Repair Disk (ERD) by clicking Start, Programs, Accessories, System Tools, and opening Backup. From the Backup window, click the button for Emergency Repair Disk and the steps.

You will need four blank, formatted, 1.44-MB floppy disks

Windows XP:

When formatting a floppy diskette, users have the option of creating a MS-DOS startup disk, follow the below steps to do this.

  • Place diskette in the computer.
  • Open My Computer, right click the A: drive and click Format.
  • In the Format window, check Create an MS-DOS startup disk.
  • Click Start

Safe Mode

Safe mode that enables you to enter safely into Windows and correct any problems that may be preventing them from entering normal mode. Safe mode is available in Microsoft Windows 95, Windows 98, Windows ME, Windows 2000, and Windows XP It is not available in Windows 3.x, and Windows NT 4.0. In Safe mode, the custom config files are skipped, and only required drivers are loaded. This helps you to correct issues so they can get back into normal mode. Usually, in Safe mode only mouse keyboard and VGA drivers are loaded.

Windows 9x:

You can enter the safe mode by pressing the F8 key as soon as the computer starts up or you see starting Windows 9x message on the screen. You will see a menu. Enter choice 3 and press enter key.

Windows 2000/XP:

You can enter the safe mode by pressing the F8 key as soon as the computer starts up or you see starting windows 2000/XP message on the screen. In the menu, use the up/down arrow keys to highlight the choice and press enter.

In Windows 2000/XP you will have 3 different choices for Safe Mode:

Safe Mode - Starts Windows 2000 using only required files and drivers (mouse, monitor; keyboard; mass storage; and no network disabled, if any).

Safe mode with Networking - Starts Windows 2000 using only required files and drivers, with network enabled.

Safe Mode with Command Prompt - Starts Windows 2000 using only required files and drivers. After logging on, you will be taken to the command prompt, where you can do necessary changes, and reboot.

Last Known Good Configuration:

Starts up Windows 2000/XP from the registry information that the Windows saved at the previous successful shutdown. Use this option only in cases of incorrect configuration. Last Known Good Configuration does not solve problems caused by corrupted or missing drivers or files. Also, any changes made since the last successful startup will be lost.

This feature is not available for Windows 9x operating systems.

Command Prompt Mode:

Starts Windows with only basic files and drivers. After logging on, the command prompt is displayed instead of the Windows desktop.

Loads the and DoubleSpace or DriveSpace files (if present). This mode is used to run recovery utilities and repair the registry. It also helps to check the integrity of the file system.

Booting to a System Restore Point:

System Restore enables restoring your computer by to its original configuration or to a configuration point that was set afterwards.

Often a restore is done because of one or more of the following reasons.

  • Serious data corruption that can not be reversed.
  • Intend to remove recently installed software and programs and get it back to how it was when you first purchased it.
  • You intend to remove all personal data because plan on selling the computer or plan on giving it away.

Recovery Console:

Recovery Console can be accessed from Windows 2000/XP setup by booting the computer with the Windows 2000/XP CDROM. On boot up, you will be presented with a choice of menu .Select Repair option by pressing R key.

The next screen provides you with two options a. Repair a Windows 2000 installation by using the Recovery Console, or b. Repair using the emergency repair process. Select Repair by Using Recovery Console and then press C to continue.

You will be requiring administrative privileges to use Recovery Console.

The following tasks may be performed using Recovery console:

  • Formatting drives
  • Read and Write Files
  • Repairing a non-booting system
  • Repairing a corrupt Master Boot Record (MBR)
  • Start and stop Services

Creating Emergency Disks with OS Utilities

ERD (Short for Emergency Repair Disk), creates backups of important system files and settings. It is useful for troubleshooting problems with Windows 2000/XP installations. The ERD is required when you go for Windows repair option. You will be prompted for the diskette when needed. The ERD is different form boot disk, as the former is used in conjunction with Windows repair.

The ERD is capable of performing such checks as:

  • Verifying the boot sector is not corrupt.
  • Repairing any startup files.
  • Locate any missing or damaged system files.

Creating Emergency repair Disk for Windows 2000:

  • Click Start > All Programs > Accessories > System tools > Backup from the menu.
  • On the tools menu click on create an emergency repair disk and follow the instructions to complete.

Creating Emergency Repair Disk for Windows NT:

You can create the Emergency repair disk while installing the operating system. The setup will guide you on how to create the repair disk.

To manually create the Emergency Boot Disk do this:

  • Click on Start the click on Run
  • In the open box type rdisk /s

In the next screen type rdisk in the Open box, and then click Update Repair Info.

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