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ATHENA-SPECIFIC GUIDE TO READING
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Introducing the Unix System
by Henry McGilton and Rachel Morgan
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March 12, 1984
Beth Anderson
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General Comments
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Unix Documentation
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The Unix operating system comes with a standard set of documentation, called
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The Unix Programmer's Manual.
This
documentation is voluminous and contains reference, historical,
and tutorial materials meant for a variety of Unix users, from
novices to programmers who intend to modify the inner workings of
the operating system.  Much of the material is also out-of-date or
inapplicable to the Athena system.
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Project Athena has reorganized and published a subset of this 
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Unix Programmer's Manual
as four main subvolumes (the Project Athena 
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Unix User's Guide,  Unix Programmer's Guide, Unix Commands,
and
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Unix Functions
manuals), plus four small manuals
for each language.  The Unix documentation remains, nonetheless, 
fragmented and reference-like; ill-suited to gaining a good perspective
on how to use the Unix system.
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By contrast, the McGilton book is a carefully-organized tutorial that
shows you step-by-step how to use Unix.  The book concentrates on
conveying those features of Unix one would expect to use most
often and most profitably.  You will find that the
McGilton book will often refer you to the
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Unix Programmer's Manual
because it
contains more-complete descriptions of the features of
Unix.  The Project Athena
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Unix Commands
and
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Unix Functions
manuals correspond to Volume 1 of the original
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Unix Programmer's Manual
that McGilton is usually pointing you towards.
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This Reading Guide
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The version of the Unix operating system 
and the set of Unix programs that the McGilton book discusses are 
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not exactly
those that Project Athena will use.  The attached Athena-specific guide
to reading the McGilton book notes the important differences.  Little harm
would be done, however, if you wished to read the McGilton book through
without consulting these notes: however, you'll have to adjust somewhat later.
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The differences center around the following areas:  
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Omissions
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The Athena
"system software" (those programs that will be available for you to use on
every Athena computer) is made up of
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a standard collection of programs
called "Unix"
plus some additional programs.  For example, we have added
a library of pre-packaged
numerical algorithms that you can use to calculate sines and cosines and
many other mathematical functions.  The McGilton book discusses only
the Unix programs.
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Two Unixes  
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In the last fifteen years, the
Unix system has evolved into several versions.  Today,
there are two
major versions of Unix: Bell Labs Unix and "Berkeley Unix" from
the University of California at Berkeley.  Project Athena uses
Berkeley Unix.  The McGilton book discusses both versions,
but concentrates on the Bell version.  
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In particular, Berkeley Unix and Bell Labs Unix have different
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shells.
When you use Unix, you will issue "commands" to do things
such as edit a document or print your mail.  These commands are interpreted
by a program called a "command interpreter" or, in
Unix, a "shell."
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Berkeley Unix comes with two alternative command interpreters: 
the original "Bourne shell" from Bell Labs
(also known as the "Version 7 shell")
and the "C shell" written at Berkeley.
While you will be using the C shell, McGilton
concentrates on the other shell, the Bourne shell.
(The major differences between
the shells are: 1) the C shell has very useful facilities that
the the Bourne shell does not, and 2) each shell has a different
language in which one can "program" the shell to do fancy
things.)  If you follow the chapter-by-chapter guide to reading
McGilton, you should have no trouble using the C shell.
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Unsupported Software
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For some basic tasks, Unix
provides alternative 
programs that perform the same basic function.  For example,
there are three different programs to send,
receive and file electronic mail.  Where there are alternative
programs, Project Athena has chosen one that the staff will support
(i.e., teach, update, fix and answer questions about).  For
example, we have chosen the 
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mh
mail handler.  In some cases the McGilton book discusses
the alternative programs that Project Athena does
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not
support.