Test Your Knowledge in Computers #600
Difficulty: Medium
Functions in C do not need be declared before they can be used.
True or False?
UNIX, Linux and the Key Differences
What is Unix?

All Unix and 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 preceived 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:
  1. Unix is a multi-user system where the resources can be shared by various system users.
  2. Unix provides multi-tasking. Users can execute many processes at the same time (practically speaking).
  3. Unix was the first computer operating system that was written in a high-level language (C Language).
  4. Unix provides a hierarchical file structure which facilitated fast data access.
  5. Unix has built-in networking functions so that computers can easily exchange information.
  6. Unix functionality can be extended through user programs built on a standard programming interface.
  7. 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:
  1. Linux, like Unix, is a multi-user system where the resources can be shared by various system users.
  2. Linux, like Unix, provides multi-tasking. Users can execute many processes at the same time (practically speaking).
  3. Linux, like Unix, was written in C.
  4. Linux, like Unix, provides a hierarchical file structure which facilitated fast data access.
  5. Linux, like Unix, has built-in networking functions so that computers can easily exchange information.
  6. 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
Dennis Ritchie

Dennis Ritchie was born on September 9, 1941 in Bronxville, New York. His father was Alistair E. Ritchie, a longtime Bell Labs scientist and co-author of The Design of Switching Circuits on switching circuit theory. As a child, Dennis moved with his family to Summit, New Jersey, where he graduated from Summit High School. He graduated from Harvard University with degrees in physics and applied mathematics.
Dennis created the C programming language, the basis of most all modern computer software including Unix and Linux.
Dennis began working at the Bell Labs Computing Sciences Research Center in 1967. In 1968, he defended his PhD thesis on "Program Structure and Computational Complexity" at Harvard under the supervision of Patrick C. Fischer. Dennis never officially received his PhD degree.
During the 1960s, Dennis Richie and Ken Thompson worked on the Multics operating system at Bell Labs. Ken Thompson, aided by Dennis and others, took an old PDP-7 machine and developed their own application programs and operating system from scratch. In 1970, Brian Kernighan suggested the name "Unix", a pun on the name "Multics". To supplement assembly language with a system-level programming language, Ken Thompson created B. Later, B was replaced by C, created by Dennis Ritchie, who continued to contribute to the development of Unix and C for many years.
During the 1970s, Dennis collaborated with James Reeds and Robert Morris on a ciphertext-only attack on the M-209 US cipher machine that could solve messages of at least 2000–2500 letters. He said that, after discussions with the NSA, they decided not to publish it because the principle was applicable to machines still in use by foreign governments. Dennis was also involved with the development of the Plan 9, the Inferno operating systems, and the programming language Limbo. As part of an AT&T restructuring in the mid-1990s, Dennis was transferred to Lucent Technologies, where he retired in 2007 as head of System Software Research Department.
Dennis Ritchie passed away or or about October 12, 2011 (70 years old) at his home in Berkeley Heights, New Jersey.
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