Microsoft KB Archive/149110

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Cannot Start Windows 95 After Using the SYS Command

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Q149110

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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:

  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 :\msdos.sys" where 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.   Rename the Msdos.sys file using the following command "ren :\msdos.sys msdos.xxx" where is the physical boot drive.   Use any editor (such as Edit.com) to create a new Msdos.sys file that contains the following text '''[Paths]

WinDir= :\

WinBootDir= :\

HostWinBootDrv= ''' where is the drive containing the Windows folder, is the Windows folder, and 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''' 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" Save and then close the Msdos.sys file. 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

Issue type :

Technology : kbWin95search kbWin95