An Apple patent filing, which was posted by the U.S. Patent and Trademark Office on August 21, described improved approaches for enabling portable user accounts. The result is that a user could carry the entire account and home directory on a portable device.

The inventors were cited as Robert T. Bowers in Cupertino and Steve Ko in San Francisco, and the initial filing was April 28, 2008.

The abstract for the patent says:

"A user account created at a multi-user computer can be stored to an external, portable data store, thereby rendering the user account portable. The multi-user computer system, e.g., through its operating system, locates user accounts on not only in local storage of the multi-user computer system, but also in any removable data storage attached to the multi-user computer system. Hence, by coupling the external, portable data store to another multi-user computer, a user is able to login to any supporting multi-user computer and be presented with their user configuration and user directory.

"Since the data store that stores the user account is not only external but also portable, a user can simply tote the data store to the location of different multi-user computers. In one embodiment, the external, portable data store can not only store the user account but can also provide general data storage. In another embodiment, the external, portable data store can be a portion of a portable computing device (e.g., media player) that provides other functionality besides data storage."

The patent acknowledges that a few sophisticated users have modified the operation of existing Mac OS X systems to enable so-called portable user accounts, but it requires specialized tools. "Thus, there is a need for improved techniques to enable user accounts to be portable such that a user can carry their user account with them and login to any multi-user computer system that supports portable user accounts," the filing states.

The patent goes on to describe the technical details required to implement this functionality.

Note that this is not quite the same as Appleis Portable Home Directory (PHD) feature available since OS X 10.4. In PHDs, a user can log into his or her account from any Mac on the network and access personal data and settings on a server. In contrast, with portable user accounts, a user could have the entire account and home directory on a portable device -- hard disk or flash drive. After connection to a host that supports the protocol, the portable account is treated it as a standard user account. That requires little more Unix finesse.