For example, logging in to a workstation can give the user access to all the appropriate things in a transparent way. Or multiple systems can share the same user name and password, so although the user signs on more than once, the userid and password is the same for each login.
While passwords are ``something you know," authentication can also be done by ``something you have" such as a smart card, or even a file on the computer (to make it seem like a single sign-on). Often these things are used in conjunction with passwords (eg: a bank card) but they can also be used alone (eg: many lab access cards do not require a PIN).
There are a number of systems which are based upon recognition rather than recall. (Examples of alternatives to traditional password systems are listed in [Sasse et al., 2001]) The Passfaces system takes further advantage of what we know about human memory by using faces. Humans have especially high facial recognition compared to recognition of objects.
It is also possible to find altnerate types of passwords which although they still require recall without cues, are easier to remember, such as graphical passwords. [Jermyn et al., 1999]
See section 4.1.3 for some other discussion of other authentication methods.
Four or five is the maximum number of unrelated, regularly-used passwords that a user can be expected to handle comfortably [Adams and Sasse, 1999]