How BIOS Password Removal Works

All laptops have to begin life somewhere, and in this case, it is the manufacturing origin. Newly manufactured motherboards usually have blank memory chips, and the programming of these flash chips occurs on a fully constructed laptop. BIOS programs, whether it is Award, or Phoenix, use hook declarations to access parameters stored in the serial flash memory chip. Many of these parameters initialise the chipset such as the video subsystem, processor, and bridge settings.

When the motherboard is new, the memory content of the serial flash chip is clear, where each bit is zero. When the BIOS hook detects null characters in the memory, it enters into "Manufacturing Mode", waiting to receive new programming. In this mode, the BIOS will store the correct parameters into the serial flash chip.

How a Serial Flash Chip Works

For a read or write operation to occur, an 8-bit address is usually first sent to the chip to select it.

A0, A1, A2 are device address pins, and the address always starts with 10000 for the most significant bits of the word. The next three bits must be the same as the hard-wired address bits. Therefore, the 8 bits are usually "10000A2A1A0" and they select the device. Up to eight devices are addressable on a single bus like this.

By feeding the clock pulse from pin 6 to the address line A2, the device address given by bits A0, A1, A2 no longer matches the hard-wired address bits, in effect, sending the wrong address. Without the chip selected, read operations cannot occur. When the BIOS program does not receive a reply, it assumes that the chip is blank and enters the manufacturing mode.

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