I've been considering trying to hack an old '98 era motherboard. The ROM(I presume for the BIOS) is a Winbond W29C020-70. In it's datasheet, there is a thing called "Software-protected Data Write". The gist of it is that 3 specific bytes must be written to certain addresses before the ROM will allow you to write to it.
The values and addresses that need to be written are documented in the datasheet, and I don't believe there is a way to change these magic values. So, using this feature for security doesn't seem likely. I can't really think of any other reason for this feature to exist.
What is the point in this kind of feature?
Best Answer
The sequence of bytes is not for hiding the content from others, but to prevent accidental overwrites of data. You can accidentally write a byte to the EEPROM, but accidentally writing the three specific bytes in a row is much less likely.
And no, you can't change the bytes.