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Configuring Startup and Troubleshooting Startup Issues : Understanding the Startup Process (part 1) - Power-on Self Test Phase, Initial Startup Phase

6/12/2013 11:33:14 AM
To diagnose and correct a startup problem, you need to understand what occurs during startup. Figure 1 provides a high-level overview of the different paths startup can take.
Figure 1. The Windows Boot Manager provides several different startup paths.


The normal startup sequence for Windows Vista is:

  1. Power-on self test (POST) phase

  2. Initial startup phase

  3. Windows Boot Manager phase

  4. Windows Boot Loader phase

  5. Kernel loading phase

  6. Logon phase

This sequence will vary if the computer is resuming from hibernation or if a non-Windows Vista option is selected during the Windows Boot Manager phase. The following sections describe the phases of a normal startup process in more detail.

1. Power-on Self Test Phase

As soon as you turn on a computer, its processor begins to carry out the programming instructions contained in the basic input/output system (BIOS) or Extensible Firmware Interface (EFI). The BIOS or EFI, which are types of firmware, contain the processor-dependent code that starts the computer regardless of the operating system installed. The first set of startup instructions is the power-on self test (POST). The POST is responsible for the following system and diagnostic functions:

  • Performs initial hardware checks, such as determining the amount of memory present

  • Verifies that the devices needed to start an operating system, such as a hard disk, are present

  • Retrieves system configuration settings from non-volatile memory, which is located on the motherboard

The contents of the non-volatile memory remain even after you shut down the computer. Examples of hardware settings stored in the non-volatile memory include device boot order and Plug and Play information.

After the motherboard POST completes, add-on adapters that have their own firmware (for example, video and hard drive controllers) carry out internal diagnostic tests.

If startup fails before or during POST, your computer is experiencing a hardware failure. Generally, the BIOS or EFI displays an error message that indicates the nature of the problem. If video is not functioning correctly, the BIOS or EFI usually indicates the nature of the failure with a series of beeps.

To access and change system and peripheral firmware settings, consult the system documentation provided by the manufacturer. 

2. Initial Startup Phase

After the POST, computers must find and load the Windows Boot Manager. Older BIOS computers and newer EFI computers do this slightly differently, as the following sections describe.

Initial Startup Phase for BIOS computers

After the POST, the settings that are stored in the non-volatile memory, such as boot order, determine the devices that the computer can use to start an operating system. In addition to floppy disks or hard disks attached to ATA, Serial ATA, and SCSI controllers, computers can typically start an operating system from other devices, such as:

  • CDs or DVDs

  • Network adapters

  • USB flash drives

  • Removable disks

  • Secondary storage devices installed in docking stations for portable computers

It is possible to specify a custom boot order, such as “CDROM, Floppy, Hard Disk.” When you specify “CDROM, Floppy, Hard Disk” as a boot order, the following events occur at startup:

  1. The computer searches the CD-ROM for bootable media. If a bootable CD or DVD is present, the computer uses the media as the startup device. Otherwise, the computer searches the next device in the boot order. You cannot use a nonbootable CD or DVD to start your system. The presence of a nonbootable CD or DVD in the CD-ROM drive can add to the time the system requires to start. If you do not intend to start the computer from CD, remove all CDs from the CD-ROM drive before restarting.

  2. The computer searches the floppy disk for bootable media. If a bootable floppy is present, the computer uses the floppy disk as the startup device and loads the first sector (sector 0, the floppy disk boot sector) into memory. Otherwise, the computer searches the next device in the boot order or displays an error message.

  3. The computer uses the hard disk as the startup device. The computer typically uses the hard disk as the startup device only when the CD-ROM drive and the floppy disk drive are empty.

There are exceptions in which code on bootable media transfers control to the hard disk. For example, when you start your system by using the bootable Windows Vista DVD, Setup checks the hard disk for Windows installations. If one is found, you have the option of bypassing DVD startup by not responding to the Press Any Key To Boot From CD or DVD prompt that appears. This prompt is actually displayed by the startup program located on the Vista DVD, not by your computer’s hardware.

If startup fails during the initial startup phase, you are experiencing a problem with the BIOS configuration, the disk subsystem, or the file system. The following a error message is common during this phase. It indicates that none of the configured bootable media types were available.

Non-system disk or disk error
Replace and press any key when ready

If you have changed the disk configuration recently, verify that all cables are properly connected and jumpers are correctly configured. If booting from the hard disk, verify that all removable media has been removed. If booting from a CD or DVD, verify that the BIOS is configured to start from the CD or DVD and that the Windows Vista media is present. If the disk subsystem and BIOS are configured correctly, the problem may be related to the file system.

If you boot from the hard disk, the computer reads the boot code instructions located on the master boot record (MBR). The MBR is the first sector of data on the startup hard disk. The MBR contains instructions (called boot code) and a table (called a partition table) that identify primary and extended partitions. The BIOS reads the MBR into memory and transfers control to the code in the MBR.

The computer then searches the partition table for the active partition, also known as a bootable partition. The first sector of the active partition contains boot code that enables the computer to do the following:

  • Read the contents of the file system used.

  • Locate and start a 16-bit stub program (Bootmgr) in the root directory of the boot volume. This stub program switches the processor into 32- or 64-bit protected mode and loads the 32- or 64-bit Windows Boot Manager, which is stored in the same bootmgr file. Once the Windows Boot Manager loads, startup is identical for both BIOS and EFI computers.

Note

The stub program is necessary because 32-bit and 64-bit computers first start in real mode. In real mode, the processor disables certain features to allow compatibility with software designed to run on 8-bit and 16-bit processors. The Windows Boot Manager is 32-bit or 64-bit, however, so the stub program sets up the BIOS computer to properly run the 32-bit or 64-bit software.


If an active partition does not exist or if boot sector information is missing or corrupt, a message similar to any of the following might appear:

  1. Invalid partition table

  2. Error loading operating system

  3. Missing operating system

If an active partition is successfully located, the code in the boot sector locates and starts Windows Boot Loader (WinLoad) and the BIOS transfers execution to it.

Initial Startup Phase for EFI Computers

Startup for EFI computers initially differs from startup for BIOS computers. EFI computers have a built-in boot manager that enables the computer’s hardware to choose from multiple operating systems based on user input. When you install Windows Vista on an EFI computer, Windows Vista adds a single entry to the EFI boot manager with the title Windows Boot Manager. This entry points to the “\Efi\Microsoft\Boot\Bootmgfw.efi” 32-bit or 64-bit EFI executable program—the Windows Boot Manager. This is the same Windows Boot Manager that is eventually loaded on BIOS-based computers. Windows Vista configures the EFI boot manager to display the EFI startup menu for only two seconds and then load the Windows Boot Manager by default to minimize complexity and startup time.

If you install a different operating system or manually change the EFI boot manager settings, EFI might no longer load the Windows Boot Manager.

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