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Q272395: Error Message: Boot Record Signature AA55 Not Found

Article: Q272395
Product(s): Microsoft Windows NT
Version(s): 2000,2000 SP1,3.51,4.0
Operating System(s): 
Keyword(s): kbsetup win95 win98 win98se w2000setup
Last Modified: 08-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.51, 4.0 
- Microsoft Windows NT Server versions 3.51, 4.0 
- Microsoft Windows NT Server, Enterprise Edition version 4.0 
- Microsoft Windows versions 2000, 2000 SP1 Professional 
- Microsoft Windows versions 2000, 2000 SP1 Advanced Server 
- Microsoft Windows 98 
- Microsoft Windows 95 
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If this article does not describe your hardware-related issue, please see the following Microsoft Web site to view more articles about hardware: 

  http://support.microsoft.com/support/windows/topics/hardware/hwddresctr.asp

SYMPTOMS
========

When you install one of the preceding Microsoft operating systems on your
computer, and then you attempt to restart your computer, you may receive one of
the following error messages:

  The system did not load because of a computer disk hardware configuration
  problem. Could not read from the selected boot disk. Check the boot path and
  disk hardware. Please check the Windows NT documentation about hardware disk
  configuration and your hardware reference manuals for additional information.
  Boot failed.

  - or -

  Boot Record Signature AA55 Not Found, xxxx Found Setup is inspecting your
  computer's hardware configuration... NTDETECT failed

  - or -

  Boot Signature AA55 Not Found Error

CAUSE
=====

This behavior can occur for one of the following two reasons:

- In Microsoft Windows NT 4.0, your attempt to restart your computer is
  unsuccessful because the operating system, located on the hard disk, is
  within a partition that is greater than 4 gigabytes (GB) in size, or the hard
  disk itself is greater than 7.8 GB in size.

  NOTE: This behavior does not occur with Microsoft Windows 2000.

- The master boot record (MBR) or a boot sector does not have a 55AA boot
  signature at the end of the sector.

  NOTE: This behavior may occur if the computer system has a virus or if the
  computer hardware malfunctions.

RESOLUTION
==========

To resolve this behavior, follow the steps in one of the following two
sections:

If Windows NT 4.0 Partition Is at Least 4.0 GB or If the Hard Disk Is Greater than 7.8 GB:
------------------------------------------------------------------------------------------

- Install Windows NT 4.0 on a partition within the first 4.0 GB of the hard
  disk and ensure that the size of the hard disk does not extend 7.8 GB.

- Since this behavior occurs while using the multi() syntax in the Boot.ini
  file, modify the Boot.ini file to use the scsi() syntax instead.

For additional information about how to modify the Boot.ini file, click the
article number below to view the article in the Microsoft Knowledge Base:

  Q102873 Boot.ini and ARC Path Naming Conventions and Usage

NOTE: Windows NT 4.0 Service Pack 4.0 contains a version of the Atapi.sys file
that enables your computer system to recognize a hard disk greater than 7.8 GB.

For additional information about the hard disk being misreported, click the
article number below to view the article in the Microsoft Knowledge Base:

  Q254769 Hard Disk Is Misreported as 8 GB in Size During Setup

If Master Boot Record Signature (for Microsoft Windows 95, Microsoft Windows 98, Microsoft Windows NT, or Microsoft Windows 2000) Is Missing:
---------------------------------------------------------------------------------------------------------------------------------------------

Use a disk editor such as Microsoft Disk Probe (runs on Windows NT) or Norton
Diskedit (runs on MS-DOS) to verify if the partition table entries are still
intact and the boot record signature (55AA) is present. The first sector, sector
0 (zero), on any hard disk contains the MBR and the partition table. The last
two bytes of sector 0 are the boot record signature bytes (55AA). If the boot
record signature is missing, use a disk editor to enter these values into the
appropriate location. However, this behavior is usually an indication that the
MBR, and possibly the partition table, are corrupt.

If the partition table is corrupt, you cannot easily rebuild it and the
instructions on how to recover the partition table are beyond the scope of this
article. However, you can easily recover a MBR that is corrupted: you must
ensure that sector 0 contains the boot record signature, and then you can safely
run the fdisk /mbr command. This command rewrites only the MBR code of sector 0
if 55AA is present at the end of the sector.

CAUTION: If 55AA is not present at the end of sector 0 and you run the preceding
command, the partition table and all the partition information on that hard disk
are destroyed.

NOTE: You can run the fdisk /mbr command from an MS-DOS, Windows 95, or Windows
98 Startup disk.

STATUS
======

Microsoft has confirmed this to be a problem in in Microsoft Windows NT.

MORE INFORMATION
================

Several components in Windows NT access the hard disk using BIOS INT13 functions
during the startup and setup processes. When the system partition goes beyond
the 4 GB "border", the startup code is modified incorrectly and the subsequent
startup process is unsuccessful. Windows NT is unaware of BIOS INT13 extensions
that are used to translate hard disk information for hard disks greater than 7.8
GB. (This behavior does not occur with Windows 2000.)

When you install Windows NT on a logical drive in an extended partition, OSLoader
needs to "walk the extended partition table" through BIOS calls to get to the
partition on which Windows NT is installed. Each of these logical drives are
addressed in a "daisy chain" of partition tables. Each sector that contains a
partition table entry must end with 55AA as the last two bytes in the sector.

The MBR consists of startup code that is used by the system BIOS to read the
partition table. From data contained in the partition table, the MBR can
determine which partition is set to be bootable (active) and what is the
starting sector of that partition. When that location is determined, the BIOS
goes to that sector and begins the next phase of the startup process by running
additional code that is operating-system specific.

If the only problem with sector 0 is that the last two bytes are not 55AA, you
can easily correct this with a disk editor. However, an error message usually
indicates that something is overwriting or destroying the entire boot sector
(sector 0), including the partition table entries.

If the MBR is corrupted and you want to quickly recover it, use the Windows NT
4.0 Resource Kit Disksave.exe utility to save a copy of the MBR to a 3.5-inch
disk. This disk can be used, if needed, to restore the MBR with the Disksave.exe
utility.

The third-party products discussed in this article are manufactured by vendors
independent of Microsoft; we make no warranty, implied or otherwise, regarding
these products' performance or reliability.


Additional query words: HWSCSI

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Keywords          : kbsetup win95 win98 win98se w2000setup 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT400search kbWinNTW351search kbWinNTW351 kbwin2000AdvServ kbwin2000AdvServSearch kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTS400 kbWinNTS351 kbwin2000Search kbwin2000ProSearch kbwin2000Pro kbWinNTS351search kbWin95search kbWin98search kbWinAdvServSearch kbZNotKeyword3 kbWin2000AdvServSP1 kbWin2000ProSP1 kbWin98
Version           : :2000,2000 SP1,3.51,4.0
Issue type        : kbprb

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