Hard Disk Passwords
The ATA-3 specification introduced new optional security features, including passwords that can be set through the BIOS or various software applications. If implemented, there are two passwords in hard disks, the user and the master passwords. The master password was designed so that a company administrator could gain access to the computer in case the user password was lost. If passwords are being used, there are two modes that the disk can operate in: high and maximum. In the high security mode, the user and master password can unlock the disk. In maximum-security mode, the user password can unlock the disk but the master password can unlock the disk only after the disk contents have been wiped. After a certain number of failed password attempts, the disk will freeze, and the system will need to be rebooted.

The hard disk will require the SECURITY_UNLOCK command to be executed with the correct password before many of the other ATA commands can be executed. After the correct password has been entered, the disk works normally until the disk is powered down.

Some ATA commands are still enabled on the hard disk when it is locked, so it may show up as a valid disk when inserted into a computer. However, when you try to read actual user data from a locked disk, it will either produce an error or require a password. There are several free programs on the Internet that will tell you if the disk is locked and will allow you to unlock it with the password. Two such programs are atapwd and hdunlock.[1] The password can be set through the BIOS or through various software applications. Some data-recovery companies may be able to bypass the password by opening the disk.

[1] These programs are most commonly found on Web sites that document how to modify video game consoles. An example is http://www.xbox-scene.com/tools/tools.php?page=harddrive.