A: Linux runs on almost every general-purpose computer made in the last 10 years. It runs on systems as small as PDAs (for example, the Sharp Zaurus) and on systems as large as IBM mainframes. There are Linux distributions specifically for mobile and handheld platforms. Information on the Linux distribution for the Compaq iPAQ is at http://www.handhelds.org.

Linux was written originally for Intel processor based PC's, using the hardware facilities of the 80386 processor and its successors to implement its features. The 80386 family includes the 80486 and all of the Pentium chips. However, there are now many ports to other hardware platforms. See Ports to Other Processors.

Refer also to the Linux INFO-SHEET for more details as well as the answers to Where Is the Documentation?, What Hardware Is Supported?, and Ports to Other Processors, below.

A: A minimal Linux installation requires a machine for which a port exists, at least 2Mb of RAM, and a single floppy drive, but to do anything even remotely useful, more RAM and disk space are needed. Refer to: Ports to Other Processors, What are the Disk Space Requirements for Minimal, Server, and Workstation Use?, and What are the Minimum and Maximum Memory Requirements?. Intel CPU, PC-compatible machines require at least an 80386 processor to run the standard Linux kernel.

Linux, including the X Window System GUI, runs on most current laptops. Refer to the answer for: How Do I Find Out If a Notebook Runs Linux?. There are numerous sources of information about specific PC's, video cards, disk controllers, and other hardware. Refer to the INFO-SHEET, Laptop-HOWTO, and the Unix-Hardware-Buyer-HOWTO. See Where Is the Documentation?.

A: At any given time, there are several "stable" versions of Linux, and one "development" version. Unlike most proprietary software, older stable versions continue to be supported for as long as there is interest, which is why multiple versions exist.

Linux version numbers follow a longstanding tradition. Each version has three numbers, i.e., X.Y.Z. The "X" is only incremented when a really significant change happens, one that makes software written for one version no longer operate correctly on the other. This happens very rarely -- in Linux's history it has happened exactly once.

The "Y" tells you which development "series" you are in. A stable kernel will always have an even number in this position, while a development kernel will always have an odd number. The "Z" specifies which exact version of the kernel you have, and it is incremented on every release.

The current stable series is 2.4.x, and the current development series is 2.5.x. However, many people continue to run 2.2.x and even 2.0.x kernels, and they als o continue to receive bugfixes. The development series is the code that the Linu x developers are actively working on, which is always available for public viewing, testing, and even use, although production use is not recommended! This is part of the "open source development" method.

Eventually, the 2.5.x development series will be "sprinkled with holy penguin pee" and become the 2.6.0 kernel and a new stable series will then be established, and a 2.7.x development series begun. Or, if any really major changes happen, it might become 3.0.0 instead, and a 3.1.x series begun.