A specific way for the Windows operating system to load when there is a system-critical problem interfering with the normal operation of Windows. Safe mode allows the user to troubleshoot the operating system to determine what is not functioning properly. For example, adding new software or drivers for a hardware device to the system can cause conflicts with existing programs. Safe mode is a way to find out what the problem is.
In safe mode, the only startup programs that are loaded are the operating system and drivers for the mouse, keyboard and standard VGA display modes. Safe mode does not run the autoexec.bat or config.sys files. The main portion of the Registry is not loaded. Himem.sys, which is normally loaded as part of the config.sys script, is loaded with the /testmem:on switch, which tells the computer to test the extended memory before continuing. Windows also boots using a batch file called system.cb instead of the standard system.ini file while in safe mode.