2x 20gb hard disks brand new, one made to be 2.1gb?

Hey,
Just wondering if anyone knows anything about this:

I've seen it a few times on hard disks that the Size of the disk is smaller then the default size that the disk sells at.

For Example;
I have 2x Seagate ST320014A by default these should be 20gb.
One of them has another part number on it "445-0654055" Stating its 2.1gb and it shows up as a 2.1gb on the computer i test it on.

But its still the exact same hard disk, i am curious if its still got a capacity of 20gb but has been coded to only allow for 2.1gb by the manufacturer.
Is this true and is there anyway of unlocking it to be 20gb if it is true?

Thanks
-Ash

Have you checked any jumpers on the disk? I remember that older disks used to have an option to limit them to 2GB as some old BIOSes couldn't handle more than that, though I'd be surprised to see that on a 20GB drive.