From: Prasanna Kumar Jayapal (prasak_at_winse.microsoft.com)
Date: Wed Jan 07 2004 - 17:07:35 PST
This paper (The UNIX Time-sharing system) discusses the key features of
the Unix operating system highlighting the concepts of File system and
its implementation, Process and Images, Shell, Standard IO and Traps.
This operating system described here was developed for DEC's PDP systems
and was written in assembly language.
This paper nicely describes the UNIX system although it is an initial
version, the features explained are the fundamental building blocks of
an operating system. It initially gives a brief overview of the history
and the environment and delves in to the File System, where the authors
explain the concepts (Files, directories, removable FS, Protection, etc)
and then the implementations of the FS. They start from the very basics
like defining a file, the Root ("/"), the current (".") and parent
("..") directories and go on to explain the i-list, i-nodes and how the
file reads and file writes work. The key thing to observe here is that
in UNIX, every object is considered as a file and contains the i-node
descriptors. Also, it was impressive to see the thought gives to the
file protection in the early stages itself. Then the author goes on to
give an overview of the process management and synchronization
mentioning some internal details and the commands. Later on they talk
about the shell, the different filter commands, and separators and
briefly mention about the multitasking and the implementation of the
shell. Then lastly they touch a little on the hardware interrupts and
how they are trapped. I think most of the features are very well
thought, nicely implemented by maintaining simplicity and is very
effective and useful even today.
Reading through the Perspective section, I was surprised to see how the
first version was started. It is indeed true that "the necessity is the
mother of invention".
Overall, I think this paper provides a very good summary of the initial
Unix system and covers the fundamentals. The important concepts of the
Operating Systems are neatly explained with good justification, design
analysis and implementation details. I feel that the authors could have
made it into two different papers, one talking about the history and the
efforts of building an operating system, its initiatives, planned
features, perspective, etc (I am a little curious on the history) and
the other could have primarily focused on the implemented UNIX system,
explaining the rationalization behind the implementation, etc. Just a
thought...
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