Plan 9 from Bell Labs

Pike, Presotto, Thompson, Trickey

Overview

   * Don't use generic workstations hooked up in a network; use dedicated
     compute servers, file servers, and terminals (memories of
     mainframes...).
   * Build a completely new system, software and hardware (but it looks a
     lot like Unix, at least superficially).
   * All services appear to be presented as a filesystem; all operations are
     performed with file operations; e.g.
        o print files by copying them into a "printer" directory
        o control processes by manipulating files in "proc" directory
        o interact with devices by accessing files in "dev" directory
   * The filesystems presented by different servers can be attached
     (mounted) together, to produce an apparent single file hierarchy,
     called a name space. Each process can have a separate name space.

The pieces

   * CPU servers
        o Expensive computing, such as compiling, is done on the CPU server,
          which is a fast multiprocessor with a very fast connection to the
          file server.
        o No local storage, except for transient "files" such as the image
          of a running process.
        o Doing work on the CPU server is merely a performance issue, not
          one of correctness: a process executing on the CPU server or on
          the user's terminal executes in the same environment.
        o No process migration; processes are explicitly started on a
          low-load CPU server, and they stay there.
        o Heterogeneity is handled with an sww-like mechanism.
   * File servers
        o Files are stored permanently on WORM drives (300GB); 600MB
          magnetic disk and 64MB RAM serve as two-level caches.
        o The high-speed connection to the CPU server makes cached files
          accessible very quickly.
        o Clients never cache data; the file server acts as a centralized
          cache, avoiding the cache consistency issue (but at what cost?).
        o The file server provides read-only access to "snapshots" of the
          filesystem as it was at certain times in the past, without any
          special dump/restore handling.
   * Terminals
        o Gnot terminals (specially designed) seem to be a lot like Sun 3's.
        o Diskless; no external storage.
        o Does not do computing; just local processing like the window
          manager.
   * Networks
        o CPU servers and file servers communicate with each other using
          20MB/s connections (that's MBytes).
        o Other links are not as critical; generally, about 120-150KB/s.

Systems

   * Proc file system is a lot like Linux's (well, the other way around).
   * Window system provides a text console, mouse input, and bitmapped
     display device for each window.