.TLPreface to the Third (2000) Edition.LPA 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 aspectof 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 andcontrol resources both local and remote..LPSome of the changes are sweeping:.IPAlef 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 onin a new thread library for C..IPSupport for color displays is much more general, building on a newalpha-blending graphical operator called.CW drawthat replaces the old.CW bitblt .Plan 9 screens are now, discreetly, colorful..IPA new mechanism called plumbing connects applications togetherin a variety of ways, most obviously in the support of multimedia..IPThe interfaces to the panoply of rotating storage devices have beenunified and extended,while providing better support for having Plan 9 coexist with otheroperating systems on a single disk..IPPerhaps most important, this release of the system is being done underan open source agreement, providing cost-free source-level access to thesoftware..LPPlan 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 graphicsand creating the new disk and bootstrap modelas well as providing a number of new commands;David Hogan ported Plan 9 to the Dec Alpha;andSape Mullender wrote the new thread library..LPOther new contributors includeBruce Ellis,Charles Forsyth,Eric Van Hensbergen,andTad Hunt..sp.in 3iBell Labs.brComputing Science Research Center.brMurray Hill NJ.brJune, 2000