Most access control programs provide a function that make it impossible to interrupt the computer's boot process. This is one of the fundamental features of a security system, but the function can easily lock up the computer if you do not do things in the correct order. When updating autoexec.bat or config.sys, you should always should always check that the function is disabled before restarting the computer. The function is disabled in different ways depending on the system. The most common method is to insert 'REM' in front of the line ‘switches /n /f’ in config.sys. This allows you to use F5 or F8 in DOS 6.x to interrupt the boot process.