User Password: The user password is also called a system password because it controls access to the entire system. Supervisor Password: This password prevents access to BIOS setup utility for preventing changing BIOS settings in the future. If the machine lets one boot but does not want to let the user into the BIOS setup utility, because of the BIOS supervisor password one possible recovery is to deliberately "damage" the CMOS checksum by doing direct port writes using DOS debug.exe command-line tool, corrupting some bytes of the checksum-protected area of the CMOS RAM at the next boot, the CMOS typically resets its setting to factory defaults. Sometimes it is enough to ground the CLK or DTA line of the I☬ (Inter-Integrated Circuit) bus of the EEPROM at the right moment during boot, this requires some precise soldering on SMD parts. In yet other cases, the EEPROM chip has to be desoldered and the data in it manually edited using a programmer. Some motherboards offer a CMOS-reset jumper or a reset button. In older computers with battery-backed RAM, removal of the battery and short circuiting the battery input terminals for a while did the job in some more modern machines this move only resets the real-time clock (RTC). To access the BIOS setup when the machine fails to operate, occasionally a drastic move is required.
Resetting the BIOS Supervisor Password With Debug Command
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