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Q122051: How Windows 95 Performs a Safe-Mode Start

Article: Q122051
Product(s): Microsoft Windows 95.x Retail Product
Version(s): Win2000:95
Operating System(s): 
Keyword(s): kbenv kbui win95
Last Modified: 17-DEC-2000

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The information in this article applies to:

- Microsoft Windows 95 
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SUMMARY
=======

This article discusses how Windows 95 boots in Safe mode. A Safe-mode boot can
be invoked in the following ways:

- By pressing F5 at the "Starting Windows 95" message.

- By pressing F8 at the "Starting Windows 95" message, and then choosing Safe
  Mode from the Windows 95 Startup menu.

- Automatically, if Windows 95 did not start on the previous attempt.

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

How Windows 95 boots in Safe mode:

1. Windows 95 bypasses the portion of the Registry that loads protected- mode
  device drivers, and bypasses the Autoexec.bat and Config.sys files.

2. Himem.sys is loaded with the /testmem:on switch. No other command-line
  switches are processed. For additional information, please see the following
  article in the Microsoft Knowledge Base:

  Q133442 Safe Mode Boot Does Not Process Machine Switch for Himem.sys

3. Ifshlp.sys is loaded. Dblbuff.sys is loaded with the /d+ switch.

4. Windows 95 obtains path information from the Msdos.sys file.

5. If Windows 95 files are found, the command "win /d:m" (which enables a
  Safe-mode boot) is executed and Command.com is skipped.

  If Windows 95 files are not found, Command.com is executed.


1. When "win /d:m" is executed, Windows 95 looks for a System.cb file in the
  Windows folder. If this file is not present, a clean System.cb file is loaded
  from memory.

  A clean System.cb file loads the following virtual device drivers (VxDs):

     mouse=*vmouse
     device=*configmg
     device=*vwin32
     device=*vfbackup
     device=*vshare
     device=*vcomm
     device=*ifsmgr
     device=*ios
     device=*vfat
     device=*vcache
     device=*vcond
     device=*int13
     device=*vxdldr
     device=*vdef
     device=*dynapage
     device=*reboot
     device=*vsd
     device=*parity
     device=*biosxlat
     device=*vmcpd
     device=*vkd
     device=*vdd
     device=*ebios
     device=*vtdapi
     device=*vmpoll
     woafont=dosapp.fon

2. After these VxDs are loaded, and just before Win.com loads the shell, the
  System.cb file is discarded and the original System.ini file is restored. If
  no System.ini file is found to restore, an empty System.ini file is created.
  The Winstart.bat file is not processed.

3. Windows 95 now uses the original registry settings and System.ini and Win.ini
  files.

  This effectively bypasses the [Boot] and [386Enh] sections of the System.ini
  file and disables all the Windows 95 protected-mode devices listed in Device
  Manager. Also, Windows 95 does not run programs listed on the "Load=" and
  "Run=" lines in the [Windows] section of the Win.ini file.

  Note that although the [Boot] section of the System.ini file is bypassed, the
  "shell=" and "drivers=" lines in the [Boot] section are processed.

4. The shell resizes the desktop to a resolution of 640 x 480.

Additional query words: w95susd

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Keywords          : kbenv kbui win95 
Technology        : kbWin95search kbZNotKeyword3
Version           : Win2000:95
Issue type        : kbinfo

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