And there's a downside to any zero-footprint operating system: Session- and configuration data is transient, because nothing is written to the hard drive, and nothing can be written to the read-only CD itself. It's not easy to make changes to the Knoppix setup; and whatever changes you do make will be lost on reboot. (There are ways around this, but they're not simple, and they involve defeating the zero-footprint nature of the default version of Knoppix.)

But as a way to demo Linux, or as an educational CD, or hardware tester or rescue system, Knoppix is really excellent. What's more, its automatic hardware-detection and configuration routines are outstanding. I truly hope they presage a far-reaching improvement in the way many Linux distributions set themselves up.

Morphix
Knoppix has gotten so much attention it's actually spawned its own variants, the most advanced of which appears to be Morphix. http://morphix.sourceforge.net/ modules/news/

Morphix is a modularized version of Debian/Knoppix. Like a power tool with interchangeable bits, the core or main Morphix module can be married to any of several additional modules that are optimized for a specific purpose--heavy graphics use, gaming, a speedy LightGUI version for use on slower hardware, and more http://morphix.sourceforge.net/ modules/mydownloads/ .

The Morphix site http://morphix.sourceforge.net offers a variety of preconfigured, zero-footprint, boot-and-run CD images, based on the major module types. This makes it very easy to switch Morphix variants--you just switch CDs and reboot, with no additional configuration needed. As with Knoppix, the entire setup-and-run process takes just a couple minutes.

But unlike Knoppix, Morphix also can easily be installed onto a hard drive, avoiding the performance bottleneck of running the operating system from a CD; and also making it simpler to save custom configurations; or to assemble exactly the modules you want if none of the preconfigured versions suit your needs.

As such, Morphix is a hybrid--it can be either a preconfigured, zero-footprint operating system, or a highly customized full install in any of several variants.

But another kind of hybrid--SuSE's Live-Eval--falls in between the zero-footprint and full install options: It's an example of a small-footprint Linux.

SUSE 8.2 Live-Eval
Knoppix and Morphix are both relatively new flavors of Linux, but SuSE http://www.suse.de/ us/index.html can trace its roots all the way back to 1992 when a group of German university students started the Society for Software and System Development (Gesellschaft fur Software- und System Entwicklung).

SuSE Live-Eval http://www.suse.de/ us/private/download/ suse_linux/index.html is a hybrid, small-footprint version of Linux that runs almost entirely from a bootable CD. Like Knoppix, SuSE Live-Eval doesn't require any partitioning of your hard drive. And although some minor user input is required as the setup progresses, SuSE's hardware-detection routines are reasonably automated and well done.

The entire setup is complete in about five minutes, and delivers a fully-configured Linux environment, running a desktop designed to be instantly familiar to Windows users, and already equipped with many tools such as Office-type applications, Web browsers, E-mail tools, games, developer tools, and more. The package of preinstalled and preconfigured software isn't quite as complete as Knoppix's, but is still instantly useful, as delivered.