Preface to the Third (2000) Edition

A great deal has happened to Plan 9 in the five years since its last release. Although much of the system will seem familiar, hardly any aspect of it is unchanged. The kernel has been heavily reworked; the graphical environment completely rewritten; many commands added, deleted, or replaced; and the libraries greatly expanded. Underneath, though, the same approach to computing remains: a distributed system that uses file-like naming to access and control resources both local and remote.

Some of the changes are sweeping:


: Alef is gone, a casualty of the cost of maintaining multiple languages, compilers, and libraries in a diverse world, but its model for processes, tasks, and communication lives on in a new thread library for C.

: Support for color displays is much more general, building on a new alpha-blending graphical operator called draw that replaces the old bitblt. Plan 9 screens are now, discreetly, colorful.

: A new mechanism called plumbing connects applications together in a variety of ways, most obviously in the support of multimedia.

: The interfaces to the panoply of rotating storage devices have been unified and extended, while providing better support for having Plan 9 coexist with other operating systems on a single disk.

: Perhaps most important, this release of the system is being done under an open source agreement, providing cost-free source-level access to the software.

Plan 9 continues to be the work of many people. Besides those mentioned in the old preface, these people deserve particular note: Russ Cox did much of the work updating the graphics and creating the new disk and bootstrap model as well as providing a number of new commands; David Hogan ported Plan 9 to the Dec Alpha; and Sape Mullender wrote the new thread library.

Other new contributors include Bruce Ellis, Charles Forsyth, Eric Van Hensbergen, and Tad Hunt.