Linux is a free "open-source" operating system based on Unix. It was initially developed by Linus Torvalds in Finland. Open-source means that anyone with computer programming skills can make improvements to Linux by making changes to the computer source code, provided they post their changes back up on the Internet for others to take advantage of.
Most computer stores sell packaged versions of Linux. They generally include Linux with some additional Linux software on a CD-ROM, as well as a printed manual. they'll often sell a box with Linux on a CD-ROM, plus other things like a printed manual. This is more convenient than waiting to download everything yourself, but can be expensive. CheapBytes offers Linux on CD - no manuals included - for as little as US$2 per CD, plus a flat shipping fee of US$5 to ship up to 18 CDs anywhere within the U.S. and Canada.
Linux comes in many distributions, developed by many different people and companies. Every distribution works differently - it's all very confusing. Some include the graphical interface, "X Window"; some are text-only. Some take up dozens of megabytes of disk space; some fit on a single floppy disk. You can read about them all at the linux.org distribution list.
Hal91 is an interesting distribution of Linux. It was brought to you by Øyvind Kolås in Norway. However, Øyvind has stopped working on hal91, and his webpage no longer even mentions it. Hal91 works on any PC with a 486 or Pentium processor. Although not as full-featured as other Linux distributions, it fits on a single floppy disk, and you don't need to modify the hard drive in any way. (You just start the computer up with your hal91 disk in the floppy drive.) It's a good way to try Linux yourself.
Note: One good alternative to hal91 is installing a Linux distribution that uses the UMSDOS (Unix under MS-DOS) filesystem. This means that it installs on a DOS/Windows-formatted disk, in a folder of your choice such as C:\LINUX, without any disk partitioning or formatting at all. There are a few of these available at http://www.linux.org/dist/english.html; the one I've tried is DragonLinux.
DragonLinux starts up faster from a hard disk than hal91starts up from a floppy. DragonLinux also includes far more software, including the X Window graphical interface in the "Full" version. Unfortunately, the Light version v2r1 is a 46MB download, and the Full version v2r1 is a whopping 284MB download! If you're willing to spend all that time downloading, you can get DragonLinux at http://www.dragonlinux.org. Be sure to read the instructions at the website to find out how to run DragonLinux once it's unzipped.
An even better alternative to either hal91 or DragonLinux is a full-fledged Linux distribution. You can obtain such a distribution by sitting through downloads ranging from 650MB to several gigabytes. You can buy a distribution of your choice on CD at your local store for $40 or more. Or, you can simply buy a book that includes a Linux distribution on CD at no extra charge - this is the best deal because it provides excellent documentation to improve your Linux experience. For more information, read on into the next section.
When you're ready for a graphical interface and additional software, it's time to move on to a full-fledged Linux distribution. Due to the fact that reading the manuals included with boxed Linux distributions is often as enjoyable as reading your local phone book, you're best off buying a clear, easy-to-read book about Linux with an included CD-ROM version of Linux itself.
If you're new to Linux, I recommend the Red Hat Linux 7.3 Bible. Unlike most other Linux books and manuals, it requires no previous Linux knowledge at all, but it has enough advanced material to teach seasoned Linux users everything they need to get the most out of Red Hat Linux. Plus, it includes the full 3-CD-ROM version of Red Hat Linux 7.3, a $60 retail product, just without any tech support. Click here to buy it from Amazon.com for $34.99. That's 30% off the regular price. Also, you'll get free shipping. You'll be fluent with Linux faster than you think.
If you already have some Linux experience and are looking for some more advanced information, spring for Running Linux. This volume is the ultimate guide to advanced Linux tasks, describing how to get optimum results from any major distribution you could possibly think of. Whether you run Slackware, Suse, or anything else, this book will guide you through all sorts of useful tasks. The sections on networking, setting up Web and FTP servers, and rebuilding the kernel are especially well-written. This book is highly useful for users of any distribution. Click here to pick up this invaluable book for just $27.97 at Amazon.com - 30% off the regular price, with all shipping costs included. You won't regret your decision.