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Linux, Outside the (x86) BoxBy Peter Seebach2005-06-29 
Big iron
In 1998, a major milestone for cross-platform Linux was the announcement of an attempt to port Linux to the IBM System/390®. Even though IBM no longer calls these machines "System/390" (they're now called zSeries), the architecture directory is still named s390. IBM refers to this port as showing up in 1999, presumably because the creation of a mailing list for discussing a port isn't quite the same as a shipping product. But, in under a year from the mailing list discussion, Linux was viable on the System/390. That's sort of cool, but most users wouldn't gain any benefit from running Linux on a bigger machine. The big surprise came when people realized they could get Linux up and running on virtual machines on a mainframe. The System/390 architecture allowed complete virtualization of the machine, including even the "privileged" instructions that simply ran inside the sandbox created for them. This allowed Linux on a System/390 to be run inside a virtual machine (or multiple virtual machines). A single physical box could run quite literally hundreds of distinct Linux servers, each entirely separated from the others. The security and administrative advantages are significant; for instance, there's simply no way for an attacker who's penetrated one virtual machine to affect another. This gives the advantages of multiple separate machines without the huge overhead of running hundreds of separate power supplies, disks, memory controllers, and so forth. This port was of particular interest to enterprise developers. It's a little pricey for home users, but it's an excellent feature for people who want to run a lot of services without worrying about security or other interactions between them. The development of Linux for mainframes showcased the beginning of the use of non-x86 hardware for more than just fun and games. This was no longer just a way of doing the same things you'd do on x86 hardware -- this was something new, interesting, and above all, innovative. Linux runs on a lot of virtualized hardware. One interesting port, user-mode Linux, runs Linux on Linux. It provides a virtualized machine that can have whatever hardware features you want, allowing the Linux kernel to be run in a safe little sandbox. It's conceptually similar to the mainframe versions, but it's aimed more at desktop users. User-mode Linux is a way to test new kernels, debug kernels, or even debug user applications. For a long time, people have used programs such as Serenity Virtual Station or VMware to provide benefits similar to those offered by mainframe Linux, or to build test systems for software tests without having to actually assemble additional machines. User-mode Linux is sometimes useful for similar tasks, but it takes a slightly different approach. Whether it's an x86 or not depends on which version you run; it's also working with PowerPC®. This makes for a low-end way to run virtualized machines. Tutorial Pages: » What is it about Linux that makes it so attractive for non-x86 platforms? » Early days » Big iron » Hardware capabilities » New life for old hardware » Just playing around » Resources First published by IBM DeveloperWorks
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