From: Nathan Dire (ndire_at_cs.washington.edu)
Date: Tue Jan 06 2004 - 23:28:12 PST
My first reaction to "The UNIX Time-Sharing System" is that the UNIX
environment has changed very little in the last 30 years. I don't know
whether this is due to the consistency and utility of the interface, a lack of
innovation in subsequent systems, or merely the early success and prevalence
of UNIX systems. In any case, it is certainly admirable that the interfaces
have proved so durable in the face of so many technological advances in
computing.
On the other hand, as a result of advances hardware, one aspect of UNIX which
certainly has changed significantly is the scale of the systems on which it
runs. The paper mentions some limits which appear quite restrictive by
today's standards: seven protection bits on files, 14 characters for file
names, and a maximum file size of 1MB. This is of course a reflection of the
"fairly severe size constraints of the system and its software", one of the
major considerations which influenced the design. These limits don't appear
to have been much trouble to extend; inodes simply have more levels of
indirection to support longer file sizes, for example.
Another major consideration in the design is that the authors wanted "to make
it easy to write, test, and run programs." While this of course makes the
system popular with the technical community, the average user often finds it
difficult to master the UNIX environment. This remains an issue even for
today's versions of UNIX.
An interesting omission in the system is user-level file locking. The authors
"take the view that locks are neither necessary nor sufficient in our
environment to prevent interference between users of the same file." I would
expect advisory locking on files to be quite useful, especially in the absence
of any other form of IPC besides pipes.
It's easy to point out what's been overlooked in this paper by looking at
modern UNIX systems. In my mind, the remarkable consistency with modern UNIX
environments is a testament to Thompson's original work.
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