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Contents of the MSDOS.SYS File

The Windows 95/98/ME setup program creates a file called MSDOS.SYS in the root folder and sets the file's attributes to Read-Only, System, and Hidden. This text file 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 personalise the boot process.

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: Windows 9x/ME Uninstall Directory. NOTE: This setting is present only if you back up your old system files when you are prompted during Windows Setup.

WinBootDir=(Windows Directory)
Default: Directory specified during Setup (for example, C:\WINDOWS)
Purpose: Lists the location of Windows 9x/ME.

WinDir=(Windows Directory)
Default: Directory specified during Setup (for example, C:\WINDOWS)
Purpose: Lists the location of the Windows 9x/ME directory specified during Setup.

The [Options] section can contain the following settings which must be manually inserted:

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 automatically runs ScanDisk but prompts you before fixing errors. This setting is used only by Windows 95 OSR 2 and Windows 98/ME.

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/ME (defaults to 0).

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 the "Starting Windows" message appears.

BootMenuDefault=(Number)
Default: 1
Purpose: Use this setting to set the default menu item for the Startup menu. 1 defaults to option 1 (normal), 3 defaults to option 3 (safe mode).

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 only works if BootMenu=1 is also present.

BootMulti=(Boolean)
Default: 1
Purpose: A setting of 0 disables the multi-boot option (meaning 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 from appearing after a system crash.

BootWin=(Boolean)
Default: 1
Purpose: A setting of 1 forces Windows to load at startup. A setting of 0 disables Windows as your default operating system (this is useful only if you have MS-DOS version 5.x or 6.x on the computer).

DoubleBuffer=(Boolean)
Default: 0
Purpose: SCSI, older ESDI/IDE/ATA and large FAT32 drives > 8 GB may need double-buffering. A setting of 1 enables auto-detect, 2 switches double-buffering on permanently, and 0 disables the option.

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.

DisableLog=(Boolean)
Default: 0
Purpose: Create BOOTLOG.TXT in C:\ root upon boot. 0 to create Bootlog.txt file, change to 1 to disable.

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.

LoadTop=(Boolean)
Default: 1
Purpose: Load COMMAND.COM or DRVSPACE.BIN at top of conventional memory (just below the 640K barrier). 1 = Enabled, 0 = Disabled.

Logo=(Boolean)
Default: 1
Purpose: A setting of 1 forces the default Windows 9x/ME logo to appear when the PC is booting. 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 Startup menu.

SystemReg=(Boolean)
Default: 0
Purpose: Scan Registry files during Windows startup. 1 = Enabled, 0 = Disabled.

Extra Characters in the MSDOS.SYS File

The MSDOS.SYS file may also contain a section with what seems to be meaningless data. This data is necessary to support older software that expects the file to be at least 1024 bytes in length.

The extra data is in the form of comments (lines that start with a ';') and so is ignored by the system when booting. If present it will normally look something like this -

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

Note - As far as I know the padding is on Windows 95/98 systems only and doesn't appear in Windows ME.

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, then click Files Or Folders.
  • In the Named box, type "MSDOS.SYS" (without quotation marks). In the Look In box, click your boot drive (usually drive C). Click the Find Now button.
  • Right-click the MSDOS.SYS file and then click Properties.
  • Click the Read-Only and Hidden check boxes to clear them 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.
  • Click the Read-Only and Hidden check boxes to select them to set these attributes for the file, and then click OK. Close the Find window.
  • Quit and then restart Windows.