How Windows 95 Performs a Safe-Mode Start

• Microsoft Windows 95

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 Registry and 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:

         ARTICLE-ID: Q133442
         TITLE     : 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.

6. 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
   

7. 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.

8. 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.

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