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6.7 Systemology
===============

This section aims at presenting some systems and pointers to
documentation.  It may help you addressing particular problems reported
by users.

   Posix-conforming systems (https://en.wikipedia.org/wiki/POSIX) are
derived from the Unix operating system
(https://en.wikipedia.org/wiki/Unix).

   The Rosetta Stone for Unix (http://bhami.com/rosetta.html) contains a
table correlating the features of various Posix-conforming systems.
Unix History (https://www.levenez.com/unix/) is a simplified diagram of
how many Unix systems were derived from each other.

   The Heirloom Project (http://heirloom.sourceforge.net/) provides some
variants of traditional implementations of Unix utilities.

Darwin
     Darwin is also known as Mac OS X.  Beware that the file system
     _can_ be case-preserving, but case insensitive.  This can cause
     nasty problems, since for instance the installation attempt for a
     package having an ‘INSTALL’ file can result in ‘make install’
     report that nothing was to be done!

     That's all dependent on whether the file system is a UFS (case
     sensitive) or HFS+ (case preserving).  By default Apple wants you
     to install the OS on HFS+.  Unfortunately, there are some pieces of
     software which really need to be built on UFS.  We may want to
     rebuild Darwin to have both UFS and HFS+ available (and put the
     /local/build tree on the UFS).

QNX 4.25
     QNX is a realtime operating system running on Intel architecture
     meant to be scalable from the small embedded systems to the hundred
     processor super-computer.  It claims to be Posix certified.  More
     information is available on the QNX home page
     (https://blackberry.qnx.com/en).

Unix version 7
     Officially this was called the "Seventh Edition" of "the UNIX
     time-sharing system" but we use the more-common name "Unix version
     7".  Documentation is available in the Unix Seventh Edition Manual
     (https://s3.amazonaws.com/plan9-bell-labs/7thEdMan/index.html).
     Previous versions of Unix are called "Unix version 6", etc., but
     they were not as widely used.