The Penguin and the Dinosaur

Think Linux is only for the PC? Think again.
That's Neat, but I Don't Have a Mainframe

Perhaps I've convinced you Linux/390 is cool, and you'd like to see it for yourself. Now, you probably have a problem: you do not have access to a System/390. There are at least three ways you can play with Linux/390 without already having an actual System/390.

The least interesting option is to do what the IBM guys did initially and download their glibc, gcc and kernel patches, and build L/390 software in a cross-compilation environment hosted under Linux/x86. Sure, this works, but it's not very much fun. For the experience, you need to be running L/390 itself, which requires a System/390.

The expensive option is to buy a mainframe. A minimal P/390 on the used market will set you back less than $10,000. That's not all that much, is it? Okay, so $10,000 might be a little steep for a neat toy.

You'd still like to play, but can't spend ten grand? How does “free” sound, then? Free, as in beer and speech. Roger Bowler has written an intensely cool emulator, Hercules, which runs under Linux and emulates either a System/370 (the previous generation of IBM mainframe) or a System/390; it also emulates many of the more common mainframe peripherals. It's open source (not GPL, but the license is quite reasonable, basically just forbidding commercial use) and very easy to build. The emulator is sufficiently thorough to boot OS/MFT (a simpler IBM mainframe OS, circa 1966) and use MFT to build and boot OS/MVT (MVS's progenitor). Work is being done to bring MVS 3.8 up on it.

More to the point, Hercules emulates a System/390 well enough to boot Linux/390. I've put up a page explaining how; see the Resources section. Currently, it's not yet useful; there is no network device emulation, so getting stuff into and out of the machine is difficult. It can, we think, be done with the supplied tools and tape image files. By the time you read this, someone will probably have figured out how to load the Marist file system onto a 3330 image, which would allow for actual development. Hopefully, it will not take too long to develop enough network support to allow the virtual S/390 to appear on the network, in the same way VMWare machines do.

Be warned: you'll need patience. On my PII-300, Hercules takes close to an hour to boot Linux, although once it's up and running, interactive performance is not actually bad at all (I started playing with Linux on a 4MB 386/25, and Hercules is no more painful than it was). Many people on the Hercules mailing list (sign up from the Hercules home page) are aggressively working on performance-tweaking Hercules, so its speed should increase significantly. The referenced page will contain updates as we turn Hercules into a reasonable development environment for L/390, so check back often.

It's a grand adventure; we're exploring new territory every day. We need your help. Hop aboard, and bring your penguins. The dinosaur doesn't bite. Honest.

Resources

Glossary

email: adam@io.com

Adam J. Thornton has been using Linux since 0.09, making him older than he cares to contemplate. He distinctly remembers thinking SLS was for sissies. When he's not hunched troglodytically in front of his monitor, he enjoys playing with his Greater Swiss Mountain Dog Vinnie, bicycling with his fiancee Amy, and drinking Scotch, but not all at the same time. Write him at adam@io.com.

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