The disk lock is a built-in security feature in the disk. It is part
of the ATA specification, and thus not specific to any brand or
device. The disk lock can be enabled and disabled by sending special
ATA commands to the drive. If a disk is locked, it will refuse all
access until it is unlocked.
Based on that I believe that it is not part of the AHCI/SATA standard, however as other comments have suggested, Full disk encryption using software like true-crypt is recommended.
While the ATA disk lock is intended to be impossible to defeat without
a valid password, there are workarounds to unlock a drive. Many data
recovery companies offer unlocking services, so while the disk
lock will deter a casual attacker, it is not secure against a
The drive is simply 'locked' whereas TrueCrypt actually encrypts the data on the drive.
In addition, You should be aware that ATA mode has noticeable performance loss over AHCI. There are a number of comparisons available online between the performance benchmarks of the two. It might be that any performance impact on your system from FDE may be negated by using AHCI mode. You will need to test for your own system.
Hope that helps,