All Unix, Linux and other Unix-like operating systems are families of computer operating
systems derived from the original Unix System from Bell Telephone
Laboratories. Today, the largest Unix descendent directly certified as
"UNIX" is macOS by Apple. The original commercial Unix derivatives included
HP-UX, AIX and SunOS, to name a few. The diversity and perceived
incompatibility between various Unix systems led to the creation of
interoperability standards including the Portable Operating System Interface
(POSIX).
Unix is the original and most powerful and popular multi-user and
multi-tasking Operating System. The basic concepts of Unix were originated
in the Multics project of 1969. The Multics system was intended as a
time-sharing system that would allow multiple users to simultaneously access
a mainframe computer. Ken Thompson, Dennis Ritchie, and others developed the
basic building blocks of Unix including a hierarchical file system and a
command line interpreter for the PDP-7. Multiple generations of Unix systems
were developed for myriad computers.
As mentioned, historical perceived incompatibility between the various early
Unix systems led to the creation of POSIX and the Single Unix Specification.
Historically, the rigid "standardization" approach led to the creation of
various open source approaches to Unix including the Free Software
Foundation (FSF), GNU and Linux. Unix programs were originally created
around core design philosophies that included requirements like single
purpose, interoperable, and working with a simple standardized text
interface. Unix systems are built around a core kernel that manages the
system and the other processes. Kernel subsystems may include process
management, file management, memory management, network management and
others.
Key Features:
Unix is a multi-user system where the resources can be shared by various
system users.
Unix provides multi-tasking. Users can execute many processes at
the same time (practically speaking).
Unix was the first computer operating system that was written in a
high-level language (C Language).
Unix provides a hierarchical file structure which facilitated fast data
access.
Unix has built-in networking functions so that computers can easily exchange
information.
Unix functionality can be extended through user programs built on a
standard programming interface.
UNIX certifies compliance with a full set of interoperability standard, managed and maintained by the Open Group, which includes, not only the kernel, but the entire operating system.
What is Linux?
Linux is a Unix-like operating system created by Linus Torvalds at the
University of Helsinki in 1991. The name Linux refers to
the Linux kernel, the software on a computer which permits applications and
users to access the devices on the computer to perform specific
functions. The development of Linux was a landmark example of global, free
and open source software collaboration. Many companies and similar numbers
of individuals have released their own version of Unix-like operating
systems based on the Linux Kernel.
Similar to Unix kernels, the Linux kernel relays instructions from an
application from the computer's processor and sends the results back to the
application.
Broader in scope than commercial Unix products, Linux has been installed on a variety of platforms including mobile phones, tablets, video game consoles, NAS storage arrays, routers and small embedded controllers.
Currently the world's largest and most powerful data centers and scientific
research centers use some "flavor" of Linux.
The development of Linux is a stellar example of the power of free and open
source software development and global human collaboration.
A Linux "distribution" is a release of a Unix-like operating system based on
the specifications of the Linux kernel.
Key Features:
Linux, like Unix, is a multi-user
system where the resources can be shared by various system users.
Linux, like Unix, provides
multi-tasking. Users can execute many processes at the same time
(practically speaking).
Linux, like Unix, was written in C.
Linux, like Unix, provides a
hierarchical file structure which facilitated fast data access.
Linux, like Unix, has built-in
networking functions so that computers can easily exchange information.
Linux, unlike UNIX, specifies only the kernel but
not the entire operating system.
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An Interest Fact about the History of Unix and Linux
Man Pages
Unix man pages did not exist during the first two years of Unix history. The first actual unix man pages were written by Dennis Ritchie and Ken Thompson at the direction of Doug McIlroy in 1971.
The Unix Programmer's Manual was first published on November 3, 1971. The Unix Programmer's Manual also contained a set of short papers describing of operating system features.
The printed version of the Unix Programmer's manual was originally contained in a single binder. As of the Programmer's Workbench (PWB/UNIX) and the 7th Edition of Research Unix these documents were split into two volumes with the printed man pages forming Volume 1.
Later versions of the Unix documentation followed the concise style of the early man pages.
Dennis Ritchie added a "How to get started" section to the Third Edition introduction.
Lorinda Cherry provided the "Purple Card" pocket reference for the Sixth and Seventh Editions. For the Fourth Edition the man pages were formatted using the troff typesetting package and its set of -man macros. These macros were completely revised between the Sixth and Seventh Editions of the Unix Programmer's Manual and have not changed much since the "good ole' days".
In the early days of Unix the availability of online documentation through a man page system was regarded as a great advance in computing. The modern descendants of 4.4BSD also distributed man pages as system documentation.
Virtually every Unix command line application comes with a man page and many Unix users perceive a command's lack of a man page as a sign of low quality. Debian, for example, has written man pages for numerous programs which originally had no man page.
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