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
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
Unix is a multi-user system where the resources can be shared by various
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
Unix has built-in networking functions so that computers can easily exchange
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
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.
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
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
A "Unix-like" operating system is an OS that behaves in a manner
similar to a Unix system but is generally not certified to conform to
the Single UNIX Specification. Then again, a "Unix-like" application
is an application that performs like the corresponding Unix command or
shell. In practical terms, there is no standard for defining the term
"Unix-like" and so you will also see terms like UN*X or *nix.
Historically, there have been myriad opinions as to the degree to
which a given operating system or an application is "Unix-like".
"Unix-like" could refer to a free or open-source operating system
inspired by the Bell Labs original Unix design. "Unix-like" might
refer to a design which emulates Unix features, similar commercial and
proprietary versions, and Unix versions based on the licensed UNIX
source code. "Unix-like", for others, simply means an operating system
is sufficiently "Unix-like" to pass certification and bear the "UNIX"
trademark. Obviously, people used to find this phrase controversial.
However, over time people realized that all the historical in-fighting
did not help the Unix brand or the community as a whole; and so the
controversy has subsided, for the most part.
"Unix-like" operating systems burst into the computing scene in the
late 1970s and early 1980s. Back then, proprietary Unix versions such
as Idris (1978), UNOS (1982), Coherent (1983), and UniFlex (1985)
marketed the functionality available to academic users of UNIX as
"Unix-like". AIX, HP-UX, IRIX, SunOS, Tru64, Ultrix, and Xenix (among
others) were developed based on relatively inexpensive AT&T commercial
binary sub-licensing of UNIX back in 1979. These licensed Unix
variations displaced most proprietary Unix clones back then.
Incompatibility issues with all these glorious "Unix" operating systems created
a need for robust interoperability standards, including POSIX and the
Single UNIX Specification. The Open Group adopted the UNIX trademark
to oversee the Single UNIX Specification and the "UNIX" name became a
certification mark for Unix system interoperability.
Dennis Ritchie, one of the original Unix legends, has publicly
stated that Unix-like systems such as Linux are de facto Unix systems.
The historical years of in-fighting and legal battles over "Unix", "Unix-like", and
"UNIX" standards arguably contributed to the overall downward
trend for Unix over the years and the rise of Linux as a dominate
"Unix-like" global operating system. In 2019, macOS has the honor of having the largest
commercial UNIX in the Unix user market. Yes, it can be confusing for many
people, especially the younger generations.
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