KB118579 - Contents of the Windows Msdos.sys File

Article ID: 118579

Article Last Modified on 1/19/2007

Microsoft Windows 95
Microsoft Windows 98 Standard Edition
Microsoft Windows 98 Second Edition
Microsoft Windows Millennium Edition

This article was previously published under Q118579

SUMMARY

The Windows Setup program creates a file called Msdos.sys in the root folder and sets the file with the Read-Only, System, and Hidden attributes. Unlike the Msdos.sys file in MS-DOS, this file is a text file. It contains a [Paths] section that lists the locations for other Windows files (such as the registry) and an [Options] section that you can use to personalize the boot process.

MORE INFORMATION

The [Paths] section can contain the following settings:

HostWinBootDrv=Root of Boot Drive
Default: C
Purpose: Specifies the location for the root of the boot drive.
UninstallDir=Root of Boot Drive
Default: C
Purpose: Specifies the location of the W95undo.dat and W95undo.ini files. These files are necessary to uninstall Windows 95.

NOTE: This setting is present only if you back up your system files when you are prompted during Windows 95 Setup.
WinBootDir=Windows Folder
Default: Folder specified during Setup (for example, C:\Windows)
Purpose: Lists the location of the necessary files for booting.
WinDir=Windows Folder
Default: Folder specified during Setup (for example, C:\Windows)
Purpose: Lists the location of the Windows 95 folder specified during Setup.

The [Options] section can contain the following settings. You must manually insert these settings if you want to use them:

AutoScan=Number
Default: 1
Purpose: Defines whether or not ScanDisk is run after a bad shutdown. A setting of 0 does not run ScanDisk; 1 prompts before running ScanDisk; 2 does not prompt before running ScanDisk but prompts you before fixing errors if any errors are found.

This setting is used only by OEM Service Release 2 and Windows 98.
BootDelay=Seconds Default: 2 Purpose: Sets the amount of time the "Starting Windows" message remains on the screen before Windows 95 continues to boot.

NOTE: BootDelay is not supported in Windows 98.
BootSafe=Boolean
Default: 0
Purpose: A setting of 1 forces your computer to boot in Safe mode.
BootGUI=Boolean
Default: 1
Purpose: A setting of 1 forces the loading of the GUI interface. A setting of 0 disables the loading of the GUI interface.
BootKeys=Boolean
Default: 1
Purpose: A setting of 1 enables the use of the function key boot options (that is, F4, F5, F6, F8, and CTRL). A setting of 0 disables the use of these function keys during the boot process

NOTE: A setting of BootKeys=0 overrides the use of BootDelay=n.
BootMenu=Boolean
Default: 0
Purpose: A setting of 1 enables the Startup menu. If this setting is 0, then you must press the F8 key when "Starting Windows 95" appears, (or press and hold the CTRL key when your Windows 98-based computer restarts) to invoke the Startup menu.
BootMenuDefault=Number
Default: 1 if the system is running correctly; 3 if the system hung in the previous instance
Purpose: Use this setting to set the default menu item for startup.
BootMenuDelay=Number
Default: 30
Purpose: This setting is used to set the number of seconds your system will pause on the Startup menu. If the number of seconds counts down to 0 without intervention, the BootMenuDefault is activated.

NOTE: This option is not functional unless BootMenu=1 has been added to the [Options] section of the Msdos.sys file.
BootMulti=Boolean
Default: 1
Purpose: A setting of 0 disables the multi-boot option. (For example, with a setting of 0 you cannot boot your previous operating system.) A setting of 1 enables the F4 and F8 keys to boot your previous operating system.
BootWarn=Boolean
Default: 1
Purpose: A setting of 0 disables the Safe-mode boot warning message and the Startup menu.
BootWin=Boolean
Default: 1
Purpose: A setting of 1 forces Windows 95 to load at startup. A setting of 0 disables Windows 95 as your default operating system (this is useful only if you have MS-DOS version 5.x or 6.x on the computer).

NOTE: Pressing F4 inverts the default only if BootMulti=1. (For example, pressing the F4 key with a setting of 0 forces Windows 95 to load.)
DoubleBuffer=Boolean
Default: 0
Purpose: A setting of 1 is a conditional setting that enables double- buffering for controllers that need it (for example, SCSI controllers). A setting of 2 is an unconditional setting that enables double-buffering regardless of whether the controller needs it or not.
DBLSpace=Boolean
Default: 1
Purpose: A setting of 1 allows the automatic loading of the DBLSPACE.BIN file. A setting of 0 prevents the automatic loading of this file.

NOTE: Windows 95 uses either Dblspace.bin or Drvspace.bin if either is present in the root folder of the boot drive at startup. To disable a compression driver from being loaded at startup, use both settings in the Msdos.sys file. For example:
DBLSpace=0
DRVSpace=0
DRVSpace=Boolean
Default: 1
Purpose: A setting of 1 allows the automatic loading of the DRVSPACE.BIN file. A setting of 0 prevents the automatic loading of this file.

NOTE: Windows 95 uses either Dblspace.bin or Drvspace.bin if either is present in the root folder of the boot drive at startup. To disable a compression driver from being loaded at startup, use both settings in the Msdos.sys file. For example:
DBLSpace=0
DRVSpace=0
LoadTop=Boolean
Default: 1
Purpose: A setting of 0 does not let Windows 95 load COMMAND.COM or DRVSPACE.BIN/DBLSPACE.BIN at the top of 640K. If you are having compatibility problems with software that makes assumptions about the available memory try setting this to 0.
Logo=Boolean
Default: 1
Purpose: A setting of 1 forces the default Windows 95 logo to appear. A setting of 0 prevents the animated logo from being displayed. A setting of 0 also avoids hooking a variety of interrupts that can create incompatibilities with certain third-party memory managers.
Network=Boolean
Default: 0
Purpose: A setting of 1 means the network was installed and adds Safe mode with network support as an option on the Windows 95 Startup menu.

Extra Characters in the Msdos.sys File

The Msdos.sys file also contains a section that contains seemingly useless information. This information is necessary to support programs that expect the Msdos.sys file to be at least 1,024 bytes in length. For example, if an antivirus program detects that the Msdos.sys file is less than 1,024 bytes, it may assume that the Msdos.sys file is infected with a virus. If you delete the Msdos.sys file your computer will not start.

The following statement, followed by a series of "X"s, appears in the Msdos.sys file:

;The following lines are required for compatibility with other programs.
;Do not remove them (Msdos.sys needs to be > 1024 bytes).

Because each line begins with a semicolon (;), the lines are not read by Windows.

How to Edit the Msdos.sys File

If you want to change any of the values in the Msdos.sys file, follow these steps to edit the file:

Click Start, point to Find, and then click Files Or Folders.
In the Named box, type msdos.sys. In the Look In box, click your boot drive (usually drive C, or drive H if drive C is compressed). Click the Find Now button.
Right-click the Msdos.sys file, and then click Properties.
Click to clear the Read-Only and Hidden check boxes to remove these attributes from the Msdos.sys file, and then click OK.
Right-click the Msdos.sys file, and then click Open With.
In the Choose the program you want to use box, click WordPad, and then click OK.
Make the changes you want to the Msdos.sys file. When you are done, save the file as a text document, and then quit WordPad.
Right-click the Msdos.sys file, and then click Properties.
Select the Read-Only and Hidden check boxes to set the attributes for the file, and then click OK. Close the Find window.
Restart Windows.

For additional information about how to determine in which folder Windows is installed, click the article number below to view the article in the Microsoft Knowledge Base:

305792 How to Determine Which Folder Windows Is Installed In

Additional query words: msdos sys

Keywords: kbdiskmemory kbenv kbfaq kbhardware kbinfo kbsetup kbtshoot KB118579