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Table of contents
1.
Introduction
2.
History of the UNIX OS
2.1.
UNIX philosophy
2.2.
SUS and POSIX
3.
UNIX-like operating systems
3.1.
What is UNIX-like?
4.
Types of UNIX operating systems
4.1.
Oracle Solaris
4.2.
Darwin
4.3.
IBM AIX
4.4.
HP-UX
4.5.
FreeBSD
4.6.
NetBSD
4.7.
Microsoft/SCO Xenix
4.8.
SGI IRIX
4.9.
TRU64 UNIX
4.10.
macOS
5.
Frequently Asked Questions
5.1.
What are the three main parts of UNIX?
5.2.
What shell does NetBSD use?
5.3.
Can macOS run programs written for Darwin?
6.
Conclusion
Last Updated: Mar 27, 2024

Types of Unix Operating System

Operating Systems

Introduction

Four decades ago, in the labs of AT&T’s Bell Laboratories, the world’s first operating system was created. Every operating system designed since owes some of its inspiration to this one. The operating system created, UNIX, had its own principles, philosophies and specifications that would go on to inform all of software history.

UNIX

Source

Let us discuss the history and philosophy of the UNIX operating system and the types of UNIX operating systems.

History of the UNIX OS

In the 1960s, MIT collaborated on a research effort with General Electric (GE) and AT&T's Bell Laboratories to develop MULTICS (Multiplexed Operating and Computing System), a new type of operating system. It was designed to be a general-purpose time-sharing utility that could be used to provide power and telephone services. Hierarchical file system, security to modular architecture (enabling additional resources while the system is operating), command processor (like a shell), dynamic linking, and online reconfiguration were only a few of the novel features introduced.

While the original OS was supposed to run on GE-645 machines, Bell Laboratories changed their minds and left the project. They took the expertise they had gained to create a new multi-task operating system: the UNICS (Uniplexed Operating and Computing System). This operating system was designed to be portable, multi-tasking, and multi-user in a time-sharing environment. Thus, the first UNIX operating system was created.

Since the late 1970s, AT&T's Bell Labs has licensed UNIX to other companies. The source code for UNIX was made open-source. This paved the way for several variants of UNIX operating systems to emerge, depending on the specifications. There are basically two versions of base UNIX: Berkley Software Distribution (BSD) and System V. In the decades since UNIX has grown to what it is today. It underwent a widespread adoption by academics and amateur tech enthusiasts that led to the development of many consumer-grade desktops that could run some version of UNIX.

System III and V Family

Source

UNIX philosophy

When writing software for Unix-like systems, software writers must adhere to a set of cultural norms called the Unix philosophy. It places importance on a simple, modular, and easy-to-maintain software structure. A concise distillation of its points is listed here:

  • Smaller is better.
  • The prototype should always be prioritized.
  • Each software should do one thing, and it should do them well.
  • Portability is more important than efficiency.
  • Make a new program rather than overburdening an existing one for a new task.
  • Use a text interface for the program because most people will have that instead of something fancier.
  • The programs you write should work well collaboratively.
  • Any output your program gives should be able to become the input for another program.

SUS and POSIX

The Single UNIX Specification (SUS) is a set of operating system standards that must be followed to be eligible to use the "UNIX" brand. "The Open Group" currently owns the UNIX®  trademark. POSIX (Portable Operating Systems Standards) is the standard used to support APIs. The Open Group offers certification procedures that allow an operating system to be recognized as UNIX® and POSIX-compliant.

Also read, Advantages of Operating System

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UNIX-like operating systems

What is UNIX-like?

Before we begin listing out the types of UNIX operating systems, we must understand what UNIX-like operating systems are. Tracking down descendants of a piece of software is a complicated, often unpredictable, process. Even the definition of the UNIX operating system has changed multiple times. Fights between AT&T’s corporate undertakings to profit off their product and Richard Stallman and other free-software advocates’ struggle to preserve the GNU agenda mar the history of the UNIX OS.

Academia is credited for inventing BSD, a Unix descendent OS. The BSD (Berkeley Software Distribution) operating system is a Unix-like, open-source operating system. Its design inspired the operating systems NetBSD, FreeBSD, and OpenBSD. While not directly related, GNU/Linux borrows a lot of functionality and design choices from the academic UNIX environment and combines it with a single kernel and GNU utilities.

While there was always a commercial branch to the development of UNIX, they were minuscule compared to what the open-source community achieved. Sun, HP, and IBM all tried their hand at creating a profitable UNIX-like operating system.

Now, let us discuss a few types of UNIX operating systems in detail.

Types of UNIX operating systems

Oracle Solaris

Solaris is one of the types of UNIX operating systems created by Sun Microsystems and based on the BSD and AT&T System V operating systems. Sun Microsystems' previous operating system was called SunOS. In 1982, the first version of SunOS based on BSD foundations was released. Sun launched the scalable processing architecture (SPARC) chip, which enabled the creation of robust, dependable, and low-cost computers. This operating system was known as SunOS until version 3.x, and after version 4.0, Sun replaced SunOS with Solaris. In 1992, the Solaris 2.0 version (SunOS 5.0) was released, based on the UNIX system V release 4.

Oracle Solaris

Solaris

OpenSolaris was an open-source project based on Solaris, but Oracle discontinued it after buying Sun Microsystems.

Darwin

Darwin is one of the types of UNIX operating systems based on NeXTSTEP, BSD, Mach, and other open-source projects. It was created in 2000 by Apple. The Darwin kernel, called XNU, is responsible for much of the DNA of the macOS.

There was an attempt by the Internet Systems Consortium to collaborate with Apple to create a community-lead OS based on Darwin called OpenDarwin. The project started in 2002 but got shut down in only four years due to Apple’s disinterest and the fact that Darwin had limited usefulness outside of its macOS functionalities.

IBM AIX

AIX (Advanced Interactive eXecutive) is an enterprise-grade OS based on UNIX System V and enhanced with 4.3BSD features. It was first released in 1986, and since then, it has seen spectacular success. The AIX was known for its security, scalability and reliability and the fact that it was the first OS to have a journaling file system.

AIX

Source

HP-UX

HP-UX, or Hewlett Packard Unix, is one of the types of UNIX operating systems based on the UNIX system V. This OS introduced access control lists for file access permissions and was known for its security management and flexible memory.

HP-UX

Source

FreeBSD

FreeBSD is a free, open-source operating system based on the Berkeley Software Distribution (BSD). It is a feature-rich OS that includes a fully functional kernel, device drivers, tools, and documentation.

Free BSD

Source

The original BSD was ported to Intel-based 80386 processors by two developers, William Jolitz and Lynne Jolitz, and given the moniker 386BSD. However, there was a disagreement over the future of the OS, and a group of 386BSD programmers branched off in a new direction. This branch was the FreeBSD. It was first officially released in late 1993. The design of FreeBSD has strongly inspired the development of the macOS.

NetBSD

NetBSD is a free and open-source operating system built on the code from the 4.4BSD and 386BSD operating systems. Portability has been the highest priority for the OS. NetBSD divides its device drivers into machine-dependent and machine-independent components using a custom hardware abstraction layer to hide the hardware access details. NetBSD has applications in large-scale server systems, desktop computers, mobile devices, and embedded systems because of its code clarity, meticulous design, and portability.

Net BSD

Source

Microsoft/SCO Xenix

UNIX mania caught up to Microsoft in the late 1970s, and they decided to licence their own UNIX-like OS from AT&T. The result was the development of Xenix. The OS was never sold directly to consumers but rather licenced to various other companies like IBM, SCO, Intel etc.

Xenix

Source

The OS was never very viable as a product, and after the breakup of AT&T, Microsoft cut their losses and sold Xenix to SCO. SCO had no better luck with the product, and Xenix was discontinued in 1991.

SGI IRIX

Silicon Graphics (SGI) created IRIX, a now-discontinued OS, that ran natively on their MIPS workstations and servers. It was one of the types of UNIX operating systems that branched from UNIX system V and included BSD extensions.

SGI IRIX

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IRIX introduced the XFS file system. The OS was one of the first to have a Graphical User Interface. It was popular among the animation and scientific visualization community. The OS was discontinued in 1998.

TRU64 UNIX

TRU64 Unix is a discontinued UNIX-like OS created by Digital Equipment Corporation and based on the Alpha Instruction Set architecture (ISA). Tru64 is based on the Open Software Foundation's (OSF) OSF/1 operating system, created to compete with the UNIX System V version.

TRU64 UNIX

Source

Hewlett-Packard now owns Tru64. Many of the capabilities of Tru64 UNIX, such as AdvFS, TruCluster, and LSM, were ported to HP's flagship UNZIX OS, HP-UX. HP discontinued Tru64 in late 2012.

macOS

Apple's macOS is a commercially available UNIX-based operating system developed and maintained by the company. The OS is deeply inspired by the previous Apple OS project, the Mac OS X. The operating systems NeXT and Darwin are significant influences on the macOS. Initially, the macOS only supported PowerPC processors, but since 2006, they have started to work with Intel too.

MAC OS

Source

The success of the macOS lies with its user-friendly and very intuitive interface that has always been cutting-edge. The current macOS version, Monterey, was released in October of 2021. This release includes features such as TestFlight, an online service to install and test mobile applications; Shortcuts, a scripting language for users to create macros for executing specific tasks and LiveText to copy text from any image.

Also read - features of operating system

Frequently Asked Questions

What are the three main parts of UNIX?

The three parts that make up the UNIX OS are the kernel, the shell and the software programs.

What shell does NetBSD use?

As its /bin/sh, NetBSD uses ash. The initial ash release has spawned a slew of forks. On FreeBSD, NetBSD, DragonFly BSD, MINIX, and some Linux systems, these ash variants are installed as the default shell (/bin/sh).

Can macOS run programs written for Darwin?

Darwin is at the heart of Mac OS X, and most applications created for it should operate well on the new operating system. However, because Darwin lacks features like Cocoa and Carbon and the Aqua graphical user interface, applications written for Mac OS X won't operate under Darwin alone.

Conclusion

This article discusses the UNIX operating system's history and philosophy and then describes several types of UNIX-like OS.

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