Newcastle Connection

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The Newcastle Connection (or UNIX United) was a software subsystem from the early 1980s that could be added to each of a set of interconnected UNIX-like systems to build a distributed system. The latter would be functionally indistinguishable, at both user- and system-level, from a conventional UNIX system.[1][2] It became a forerunner of Sun Microsystems' Network File System (NFS). The name derives from the research group at Newcastle University, under Brian Randell, which developed it.

The term "UNIX United" describes the scheme of combining the overall filesystems of the participating UNIX machines; "Newcastle Connection" describes the underlying communication layer which enables this.[3] A UNIX United system constructed with the Newcastle Connection is functionally indistinguishable from a centralised UNIX system at the system-call level.[4]

In essence, the concept of the "parent directory" was re-interpreted at the root of the filesystem, where it originally had no significant meaning, to mean "this directory is on a remote machine", similar to subsequent "Super-root (Unix)" usage.

As a reminder, a typical single UNIX directory tree might resemble:

  • /
    • home
      • brian (current directory '.')
        • a
        • b

UNIX United acts as an extra level above the / root. If the example machine is named "unix1", an overall UNIX United scheme with an additional second machine, "unix2", would look like:

  • /..
    • unix1
      • home
        • brian (the current directory '.')
          • a
          • b
    • unix2
      • home
        • brian
          • b
          • c

If we wish to copy file a from "unix1" to "unix2" to sit alongside files b and c, example equivalent commands might be:

  • cp /home/brian/a /../unix2/home/brian/a
  • cp a /../unix2/home/brian/a
  • ( cd /../unix2/home/brian ; cp /../unix1/home/brian/a a )

Internals

Portability

References

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