Scenario one: You're in charge of an open computer lab at a public library. The users in the lab must have the ability to customize the computers over the course of their session, but you want to make sure any modifications they make, whether accidental or intentional, won't become permanent. The changes they make must disappear once the computer reboots so that the next user on the system will receive a "clean" home directory with the default user environment.

Scenario two: You're in charge of an open computer lab at a school. When students come in, they can sign on as either user math or english for a predefined selection of subject-related applications. As with the library scenario, the students don't have individual login names and passwords, and you don't want the students' choice of desktop or downloads to stay on the machine permanently. Every time a math student signs on as user math, the user receives a "clean" default configuration.

This second scenario describes my own work environment. As part of my job at Evergreen Valley College (San Jose, California), I administer a computer classroom with 30 dual-boot computers (Windows XP and Linux). To make sure students using Windows have a uniform experience every time they sign on, the computers have a product named Deep Freeze[1] that makes sure any changes to the computer's configuration, whether accidental or purposeful, disappear when the computer is rebooted.

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