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Q149110: Cannot Start Windows 95 After Using the SYS Command

Article: Q149110
Product(s): Microsoft Windows 95.x Retail Product
Version(s): 95
Operating System(s): 
Keyword(s): kbenv win95
Last Modified: 17-DEC-2000

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The information in this article applies to:

- Microsoft Windows 95 
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SYMPTOMS
========

When you use the SYS command to replace the Windows 95 system files on your hard
disk, the Msdos.sys file may not be replaced, or may be replaced with an
incomplete Msdos.sys file that contains only the text ";SYS."

If the existing Msdos.sys file on your hard disk is damaged and is not replaced
by the SYS command, or if the existing Msdos.sys file is replaced with an
incomplete Msdos.sys file, Windows 95 may boot only to a command prompt the next
time you start Windows 95. If the existing Msdos.sys file is not damaged and is
not replaced by the SYS command, no problems occur.

CAUSE
=====

If the SYS command (Sys.com) included with Windows 95 determines that the
existing Msdos.sys file is from MS-DOS version 6.22 or earlier, it replaces the
existing Msdos.sys file with an incomplete Msdos.sys file that contains only the
text ";SYS." If the SYS command is unable to determine that the existing
Msdos.sys file is from MS-DOS version 6.22 or earlier, it assumes that the file
is a valid Windows 95 Msdos.sys file and does not replace it.

RESOLUTION
==========

To work around this issue, manually rebuild the Msdos.sys file on your hard disk
so that it includes the location of your Windows folder and the Windows 95
system files. To do so, follow these steps:

1. Remove the system, hidden, and read-only attributes from the Msdos.sys file
  in the root folder of the boot drive. To do so, type the following command at
  the command prompt

  " attrib -s -h -r <drive>:\msdos.sys " (without the quotation marks)

  where <drive> is the physical boot drive.

  NOTE: If drive C is compressed and is currently mounted, the Msdos.sys file is
  located on the host drive for drive C. If drive C is not compressed or is not
  currently mounted, the Msdos.sys file is located on drive C.

2. Rename the Msdos.sys file using the following command

  " ren <drive>:\msdos.sys msdos.xxx " (without the quotation marks)

  where <drive> is the physical boot drive.

3. Use any editor (such as Edit.com) to create a new Msdos.sys file that
  contains the following text

  " [Paths]
  WinDir=<drive>:\<windows>
  WinBootDir=<drive>:\<windows>
  HostWinBootDrv=<boot drive> " (without the quotation marks)

  where <drive> is the drive containing the Windows folder,
  <windows> is the Windows folder, and <boot drive> is the physical
  boot drive. For example, if you installed Windows 95 on drive C in a folder
  named Windows and drive C is not compressed, the Msdos.sys file should
  contain the following lines:

  " [Paths]
  WinDir=C:\WINDOWS
  WinBootDir=C:\WINDOWS
  HostWinBootDrv=C " (without the quotation marks)

  NOTE: You can also add an [Options] section to the Msdos.sys file with
  additional settings to personalize the boot process. For information about
  the [Options] section, please see the following article in the Microsoft
  Knowledge Base:

  Q118579 Contents of the Windows Msdos.sys File

4. Save and then close the Msdos.sys file.

5. Restart your computer.

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

When you use the SYS command to replace the Windows 95 system files on your hard
disk, the SYS command replaces the existing Msdos.sys file only if it determines
that the file is from MS-DOS version 6.22 or earlier. To determine if the
Msdos.sys file is from MS-DOS version 6.22 or earlier, the SYS command checks to
see if the first byte in the file is 0x3Bh, 0xE9h, or 0xEBh. These hexadecimal
values indicate that the file is a binary file and that it is likely a valid
Msdos.sys file.

This logic is intended to prevent the SYS command from replacing a valid Windows
95 Msdos.sys file. However, when the SYS command replaces the existing Msdos.sys
file, it replaces the file with an Msdos.sys file that contains only the text
";SYS." Creating an Msdos.sys file without a [Paths] section is appropriate when
you are replacing the Windows 95 system files on a floppy disk, because the
location of the Windows folder may not be the same on the computer used to
create the bootable floppy disk and the computer on which the floppy disk is
used. Creating an Msdos.sys file without a [Paths] section is not appropriate
when you are replacing the system files on a hard disk, but the SYS command
cannot distinguish between a floppy disk and a hard disk.

If the first byte in the existing Msdos.sys file is not one of the hexadecimal
values listed above, the SYS command assumes that the file is a valid Windows 95
Msdos.sys file and does not replace it. Therefore, if the existing Msdos.sys
file is an ASCII text file, or if it is damaged (and the first character in the
file does not happen to be one of the hexadecimal values listed above), the file
is not replaced.

Additional query words: corrupted

======================================================================
Keywords          : kbenv win95 
Technology        : kbWin95search kbZNotKeyword3
Version           : 95

=============================================================================

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