How do user accounts function with external hard drives?

Question

I realized in the help menu that it implies that users can be setup with AEBS and external drives... and with the internal drive of a TC. Since I only have a TC, the thing I noticed is that when I setup a User, it seems to exist on the internal drive. It is not obvious to me that the external drive also has a user folder... it may not. The instructions are very much NOT specific... does anyone have any idea how this really works internally in the TC... and how does that compare to an AEBS with two USB drives?
Thanks...

Answer 1

This is the only pertinent information in the pdf manual.
58 Chapter 3 AirPort Network Designs
To share a USB hard disk on you network:
1 Plug the hard disk into the USB port on the back of the base station.
2 Open AirPort Utility, located in the Utilities folder in the Applications folder on a Mac, or
in Start > All Programs > AirPort on a Windows computer.
3 Select your base station, and then choose Manual Setup from the Base Station menu,
or double-click the base station to open its configuration in a separate window. Enter
the base station password if necessary.
4 Click the Disks button, and then click File Sharing.
5 Choose “With a disk password,” or “With base station password” if you want to secure
the shared disk with a password, or choose “With accounts” if you want to secure the
disk using accounts.
 If you choose to use accounts, click Configure Accounts, click the Add button, and
then enter a name and password for each user that will access the disk.
6 Choose “Not allowed,” “Read only,” or “Read and write” to assign guest access to the
disk.
7 Select the “Share disks over Ethernet WAN port” checkbox if you want to provide
remote access to the disk over the WAN port.