msdos.sys
The msdos.sys file is used to create the initial real-mode environment for Windows 9x. In MS-DOS 6.x and earlier versions this file was a binary file, but in Windows 9x this file is an ASCII file. If you open msdos.sys with any text editor (such as edit.com or Notepad) you will be able to see the current settings. You will also see a message stating that you should not delete the rows of x's. Some anti-virus and other programs check the size of msdos.sys to ensure that it has not been tampered with. Oddly enough, these programs are really only testing for a minimum file size of 1,024 bytes. There are many settings that can be changed by editing the values found in this file.
The msdos.sys file has two major sections and resembles an .ini file, which is a standard Windows file that is used to store settings. The two sections are [Paths] and [Options]. The Paths section contains information about where Windows 9x is installed (Table below lists these settings).
Paths for msdos.sys| Value | Description |
|---|---|
| WinDir | This is the Windows directory where most of the operating system files are run from. Default value is C:\Windows. |
| WinBootDir | This is usually the same location as WinDir. This option individually denotes the location of specific startup files. If WinDir is located on a drive other than C:, then WinBootDir may point to a location on the C: drive. Default value is C:\Windows. |
| HostWinBootDrv | This is the drive letter associated with the WinBootDir. Default value is C. |
| UninstallDir | This is the location of the files that should be replaced in the event of an uninstall of Windows 9x. The files are stored in w9xundo.dat and the original location information is stored in w9xundo.ini. Default value is C. |
The Options section contains options about the boot process (Table below lists these settings). Most options only have two settings, 0 which is disabled and 1 which is enabled; if the option has additional settings, they are listed in the table.
Options for msdos.sys| Option | Description |
|---|---|
| AutoScan | Windows 95-OSR2 and Windows 98 support the automatic running of Scandisk. If this is set to 0, then scandisk.exe is disabled. A setting of 1 prompts the user to scan the system after an improper shutdown, while a setting of 2 will scan automatically. Default value is 1. |
| BootDelay | This sets the length of time (in seconds) that you have to press one of the boot keys when you see the text "Starting Windows 95 . . ." at boot. Default value is 2. |
| BootSafe | A setting of 1 forces a safe mode boot of Windows 9x. Default value is 0. |
| BootGUI | A setting of 0 will cause the boot process to stop after processing autoexec.bat. You will be able to launch Windows 9x by typing WIN. This is useful during troubleshooting the boot process. Default value is 1. |
| BootKeys | Enables (1) or disables (0) the ability to press the boot keys during boot. The boot keys include F8, F5, F6, and the Ctrl key. Default value is 1. |
| BootMenu | Automatically displays the Windows 9x boot menu if set to 1. Default value is 0. |
| BootMenuDefault | Automatically pre-selects a choice in the boot menu. Default value is 1. |
| BootMenuDelay | Sets the timeout value for the boot menu. Default value is 30. |
| BootMulti | Enables the option in the boot to the previous version of MS-DOS when set to 1. This option should not be enabled on OEM versions of Windows 9x, as they do not have a previous version of MS-DOS. Default value is 1. |
| BootWarn | Enables the Safe-Mode warning message when set to 1. Default value is 1. |
| BootWin | A setting of BootWin = 0 will cause the system to automatically boot to the previous version of MS-DOS. This option should not been abled on OEM versions of Windows 9x. Default value is 1. |
| DoubleBuffer | Enables the double-buffering driver for SCSI controllers when set to 1. Default value is 0. |
| DBLSpace | Loads the Double Space driver (dblspace.bin) if it exists on the root of your drive, when this is set to 1. Default value is 1. |
| DRVSpace | Loads the Drive Space driver (drvspace.bin) if it exists on the root of your drive, when this is set to 1. Default value is 1. |
| LoadTop | By default, Windows 9x will load command.com and drvspace.bin to the top of the 640K memory range. A value of 0 causes these files to load at the bottom of the range. Some applications, such as the Novell Netware client, require that command.com be loaded low. Default value is 1. |
| Logo | A value of 0 will disable the animated logo. The animated logo can cause problems with some TSR (Terminate Stay Resident) programs or memory managers. Default value is 1. |
| Network | A value of 1 will load network support when entering Safe Mode. Default value is 0. |
Remember Windows 2000 and Windows XP boot processes do not use the msdos.sys file.
In this tutorial:
- System Files and the Boot Process
- Power-On Self-Test (POST) Process
- Standard Boot Process for Windows XP
- ntbootdd.sys
- ARC pathnames
- ntdetect.com
- The device load process
- Loading the shell
- Understanding the Boot Process for MS-DOS and Windows 9x
- msdos.sys
- config.sys
- command.com
- autoexec.bat
- win.com and vmm32
- Managing Memory
- Expanded memory
- Upper memory
- himem.sys
- Examining Other Boot Process Files
- system.ini
- win.ini