From: Joanna Muench (joannam_at_spro.net)
Date: Wed Jan 07 2004 - 17:38:21 PST
Ritchie and Thompson present an overview of the file system and user
command interface for the PDP-11 UNIX system, the third version of UNIX
built by DEC. They briefly describe the hardware needs of the system, a
mere 50K of core memory, and the interfaces and devices available. The
heart of the paper describes the file system and its implementation. A
key feature of UNIX is the assignment of file names to I/O devices as
well as physical core memory. This both simplifies programming and
allows a single protection mechanism. The implementation of this file
system by use of i-nodes allows seamless access to a file whether an
ordinary file, I/O device or mounted device. Finally the authors discuss
how processes are handled and give an overview of the shell environment.
As an intermittent user of LINUX/UNIX I found this paper
thought-provoking and informative. Reading the paper reminded me that
all these core features of UNIX were someone's design decision, long
ago. Although terse, the shell commands remain extremely powerful tools
for programming. The protection scheme has undergone some change, with
the addition of the 'group' concept and (I believe) alteration of the
set-user-id feature. Unfortunately the codes used in permission settings
have not been improved and tend to be opaque to people unfamiliar to
UNIX.
While the paper describes many important components of the UNIX system
it does not provide much in the way of motivation or philosophy guiding
the development of UNIX. It briefly mentions characteristics such as
simplicity, elegance and ease of use, but does not explain design
trade-offs required to provide these features to the user. Without these
explanations or any critique of choices made, the paper lacks a critical
viewpoint. Still it provides an excellent review of UNIX and wonderful
reminder of how much bigger, faster and cheaper our current computing
resources are.
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