1.TL 2Preface to the Second (1995) Edition 3.PP 4Plan 9 was born in the same lab where Unix began. 5Old Unix hands will recognize the cultural heritage in this manual, 6where venerable Unix commands live on, 7described in the classic Unix style. Underneath, though, lies 8a new kind of system, organized around communication and 9naming rather than files and processes. 10.PP 11In Plan 9, distributed computing is a central premise, 12not an evolutionary add-on. The system relies on a 13uniform protocol to refer to and communicate 14with objects, whether they be data or processes, and whether or 15not they live on the same machine or even similar machines. 16A single paradigm (writing to named places) unifies 17all kinds of control and interprocess signaling. 18.PP 19Name spaces can be built arbitrarily. In particular all 20programs available to a given user are customarily united 21in a single logical directory. 22Temporary files and 23untrusted activities can be confined in isolated spaces. 24When a portable machine connects to the 25central, archival file system, the machine's local 26name space is joined smoothly to that of the archival file system. 27The architecture affords other unusual abilities, including: 28.IP 29Objects in name spaces imported from other machines (even from 30foreign systems such as MS-DOS) are transparently accessible. 31.IP 32Windows appear in name spaces on a par with files and processes. 33.IP 34A historical file system allows one to navigate 35the archival file system in time as well as in space; 36backup files are always at hand. 37.IP 38A debugger can handle simultaneously active processes 39on disparate kinds of hardware. 40.PP 41The character set of Plan 9 is Unicode, which 42covers most of the world's major scripts. 43The system has its own programming languages: 44a dialect of C with simple inheritance, a simplified shell, 45and a CSP-like concurrent language, Alef. 46An ANSI-POSIX emulator (APE) admits unreconstructed Unix code. 47.PP 48Plan 9 is the work of many people. 49The protocol was begun by Ken Thompson; naming 50was integrated by Rob Pike and networking by Dave Presotto. 51Phil Winterbottom simplified the management of name spaces 52and re-engineered the system. 53They were joined by Tom Killian, Jim McKie, and Howard Trickey in 54bringing the system up on various machines and making 55device drivers. 56Thompson made the C compiler; 57Pike, window systems; 58Tom Duff, the shell and raster graphics; 59Winterbottom, Alef; 60Trickey, Duff, and Andrew Hume, APE. 61Bob Flandrena ported a myriad of 62programs to Plan 9. 63Other contributors include 64Alan Berenbaum, 65Lorinda Cherry, 66Bill Cheswick, 67Sean Dorward, 68David Gay, 69Paul Glick, 70Eric Grosse, 71John Hobby, 72Gerard Holzmann, 73Brian Kernighan, 74Bart Locanthi, 75Doug McIlroy, 76Judy Paone, 77Sean Quinlan, 78Bob Restrick, 79Dennis Ritchie, 80Bjarne Stroustrup, 81and 82Cliff Young. 83.PP 84Plan 9 is made available as is, without formal support, but 85substantial comments or contributions may be communicated to 86the authors. 87.sp 88.in 4i 89Doug McIlroy 90.br 91March, 1995 92