Hi
HDD Password is stored in the HDD unit itself.
So even the HDD unit is removed from one computer and attached to another, the HDD password is required to access it.
Here are some details:
What is A HDD Password?
http://aps2.toshiba-tro.de/kb0/FAQ9202JG0000R01.htm
TOSHIBA HDD Password summary
http://aps2.toshiba-tro.de/kb0/TSB6B01MC000CR01.htm
Note: you will not be able to access the HDD if you forget the password! So be careful with that!