DOCUMENT:Q145941 08-AUG-2001 [winnt] TITLE :Cannot Boot to MS-DOS On a Windows NT Mirrored FAT Partition PRODUCT :Microsoft Windows NT PROD/VER:3.50 3.51 OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Server versions 3.5, 3.51, 4.0 ------------------------------------------------------------------------------- SYMPTOMS ======== Windows NT allows you to dual boot between Windows NT and another operating system, such as Windows 95 or MS-DOS. However, if you establish a mirror on the system partition that contains the two operating system files, MS-DOS stops responding (hangs) after it displays "Starting MS-DOS..." and the following appears when you start Windows 95: The following file is missing or corrupt: Command.com Type the name of the command interpreter. CAUSE ===== MS-DOS looks for the System ID Byte in the partition table to determine what type of FAT file system to use. The system ID byte has three valid values that MS-DOS can determine: Value File System ----- ----------- 0x01 MS-DOS 12 Bit FAT 0x04 MS-DOS 16 Bit FAT 0x06 MS-DOS 16 Bit FAT (Greater than 32 MB in size) When you set up fault tolerance in Windows NT on a FAT system partition, the high order bit of the system ID byte changes to 0x86, which MS-DOS does not recognize. RESOLUTION ========== To work around this problem: 1. Use Disk Administrator to break the mirror and shut down Windows NT. 2. Reboot the computer and start MS-DOS or Windows 95. NOTE: You may install Windows NT to another partition and establish the mirror. Additional query words: prodnt ====================================================================== Keywords : Technology : kbWinNTsearch kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search Version : 3.50 3.51 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.