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Thursday, March 7, 2019

Chrome OS

From Wikipedia, the free encyclopedia

Chrome OS
Google Chrome logo and wordmark (2015).png
DeveloperGoogle
Written inC, C++
OS familyLinux
Working statePreinstalled on Chromebooks, Chromeboxes, Chromebits, Chromebase
Initial releaseJune 15, 2011; 7 years ago
Latest release72.0.3626.122
Latest preview
Beta
73.0.3683.67
Dev
74.0.3713.0
Update methodRolling release
Platformsx86, ARMv7, x64
Kernel typeMonolithic (Linux kernel)
Default user interfaceWIMP-based [web browser] windows
LicenseGoogle Chrome OS Terms of Service
Official websitewww.google.com/chromebook/

Chrome OS is an operating system designed by Google that is based on the Linux kernel and uses the Google Chrome web browser as its principal user interface. As a result, Chrome OS primarily supports web applications.

Google announced the project in July 2009, conceiving it as an operating system in which both applications and user data reside in the cloud: hence Chrome OS primarily runs web applications. Source code and a public demo came that November. The first Chrome OS laptop, known as a Chromebook, arrived in May 2011. Initial Chromebook shipments from Samsung and Acer occurred in July 2011.

Chrome OS has an integrated media player and file manager. It supports Chrome Apps, which resemble native applications, as well as remote access to the desktop. Android applications started to become available for the operating system in 2014, and in 2016, access to Android apps in the entire Google Play Store was introduced on supported Chrome OS devices. Reception was initially skeptical, with some observers arguing that a browser running on any operating system was functionally equivalent. As more Chrome OS machines have entered the market, the operating system is now seldom evaluated apart from the hardware that runs it.

Chrome OS is only available pre-installed on hardware from Google manufacturing partners, but there are unofficial methods that allow it to be installed in other equipment. An open source equivalent, Chromium OS, can be compiled from downloaded source code. Early on, Google provided design goals for Chrome OS, but has not otherwise released a technical description.

History

Google announced Chrome OS on July 7, 2009, describing it as an operating system in which both applications and user data reside in the cloud. To ascertain marketing requirements, the company relied on informal metrics, including monitoring the usage patterns of some 200 Chrome OS machines used by Google employees. Developers also noted their own usage patterns. Matthew Papakipos, former engineering director for the Chrome OS project, put three machines in his house and found himself logging in for brief sessions: to make a single search query or send a short email.

Chrome OS was initially intended for secondary devices like netbooks, not as a user's primary PC. While Chrome OS supports hard disk drives, Google has requested that its hardware partners use solid-state drives "for performance and reliability reasons" as well as the lower capacity requirements inherent in an operating system that accesses applications and most user data on remote servers. In November 2009 Matthew Papakipos, engineering director for the Chrome OS, claimed that the Chrome OS consumes one-sixtieth as much drive space as Windows 7. The recovery images Google provides for Chrome OS range between 1 and 3 GB.

On November 19, 2009, Google released Chrome OS's source code as the Chromium OS project. At a November 19, 2009, news conference, Sundar Pichai, at the time Google's vice president overseeing Chrome, demonstrated an early version of the operating system. He previewed a desktop which looked very similar to the Chrome browser, and in addition to the regular browser tabs, also had application tabs, which take less space and can be pinned for easier access. At the conference, the operating system booted up in seven seconds, a time Google said it would work to reduce. Additionally, Chris Kenyon, vice president of OEM services at Canonical Ltd, announced that Canonical was under contract to contribute engineering resources to the project with the intent to build on existing open source components and tools where feasible.

Early Chromebooks

In 2010, Google released the unbranded Cr-48 Chromebook in a pilot program. The launch date for retail hardware featuring Chrome OS was delayed from late 2010 until the next year. On 11 May 2011, Google announced two Chromebooks from Acer and Samsung at Google I/O. The Samsung model was released on 15 June 2011, but the Acer was delayed until mid-July. In August 2011, Netflix announced official support for Chrome OS through its streaming service, allowing Chromebooks to watch streaming movies and TV shows via Netflix. At the time, other devices had to use Microsoft Silverlight to play videos from Netflix. Later in that same month, Citrix released a client application for Chrome OS, allowing Chromebooks to access Windows applications and desktops remotely. Dublin City University became the first educational institution in Europe to provide Chromebooks for its students when it announced an agreement with Google in September 2011.

Expansion

Samsung Chromebook
 
By 2012, demand for Chromebooks had begun to grow, and Google announced a new range of devices, designed and manufactured by Samsung. In so doing, they also released the first Chromebox, the Samsung Series 3, which was Chrome OS's entrance into the world of desktop computers. Although they were faster than the previous range of devices, they were still underpowered compared to other desktops and laptops of the time, fitting in more closely with the Netbook market. Only months later, in October, Samsung and Google released a new Chromebook at a significantly lower price point ($250, compared to the previous Series 5 Chromebooks' $450). It was the first Chromebook to use an ARM processor, one from Samsung's Exynos line. In order to reduce the price, Google and Samsung also reduced the memory and screen resolution of the device. An advantage of using the ARM processor, however, was that the Chromebook didn't require a fan. Acer followed quickly after with the C7 Chromebook, priced even lower ($199), but containing an Intel Celeron processor. One notable way which Samsung reduced the cost of the C7 was to use a laptop hard disk rather than a solid state drive

In April 2012, Google made the first update to Chrome OS's user interface since the operating system had launched, introducing a hardware-accelerated window manager called "Aura" along with a conventional taskbar. The additions marked a departure from the operating system's original concept of a single browser with tabs and gave Chrome OS the look and feel of a more conventional desktop operating system. "In a way, this almost feels as if Google is admitting defeat here", wrote Frederic Lardinois on TechCrunch. He argued that Google had traded its original version of simplicity for greater functionality. "That’s not necessarily a bad thing, though, and may just help Chrome OS gain more mainstream acceptance as new users will surely find it to be a more familiar experience." Lenovo and HP followed Samsung and Acer in manufacturing Chromebooks in early 2013 with their own models. Lenovo specifically targeted their Chromebook at students, headlining their press release with "Lenovo Introduces Rugged ThinkPad Chromebook for Schools".

When Google released Google Drive, they also included Drive integration in the next version of Chrome OS (version 20), released in July 2012. While Chrome OS had supported Flash since 2010, by the end of 2012 it had been fully sandboxed, preventing issues with Flash from affecting other parts of Chrome OS. This affected all versions of Chrome including Chrome OS.

Chromebook Pixel

Chromebook Pixel (WiFi) open

Up to this point, Google had never made their own Chrome OS device. Instead, Chrome OS devices were much more similar to their Nexus line of Android phones, with each Chrome OS device being designed, manufactured, and marketed by third party manufacturers, but with Google controlling the software. However, in February 2013 this changed when Google released the Chromebook Pixel. The Chromebook Pixel was a departure from previous devices. Not only was it entirely Google-branded, but it contained an Intel i5 processor, a high-resolution (2,560x1,700) touchscreen display, and came at a price point more competitive with business laptops.

Controversial Popularity

By the end of 2013, analysts were undecided on the future of Chrome OS. Although there had been articles predicting the demise of Chrome OS since 2009, Chrome OS device sales continued to increase substantially year-over-year. In mid 2014, Time Magazine published an article titled "Depending on Who's Counting, Chromebooks are Either an Enormous Hit or Totally Irrelevant", which detailed the differences in opinion. This controversy was further spurred by the fact that Intel seemed to decide Chrome OS was a beneficial market for it, holding their own Chrome OS events where they announced new Intel-based Chromebooks, Chromeboxes, and an all-in-one from LG called the Chromebase.

Seizing the opportunity created by the end of life for Windows XP, Google pushed hard to sell Chromebooks to businesses, offering significant discounts in early 2014.

Pwnium competition

In March 2014, Google hosted a hacking contest aimed at computer security experts called "Pwnium". Similar to the Pwn2Own contest, they invited hackers from around the world to find exploits in Chrome OS, with prizes available for attacks. Two exploits were demonstrated there, and a third was demonstrated at that year's Pwn2Own competition. Google patched the issues within a week.

Material Design and App Runtime for Chrome

Although the Google Native Client has been available on Chrome OS since 2010, there originally were few Native Client apps available, and most Chrome OS apps were still web apps. However, in June 2014, Google announced at Google I/O that Chrome OS would both synchronise with Android phones to share notifications and begin to run Android apps, installed directly from the Google Play Store. This, along with the broadening selection of Chromebooks, provided an interesting future for Chrome OS.

At the same time, Google was also moving towards the then-new Material Design visual language for its products, which it would bring to its web products as well as Android Lollipop. One of the first Material Design items to come to Chrome OS was a new default wallpaper, though Google did release some screenshots of a Material Design experiment for Chrome OS that never made it into the stable version.

Chromebox for Meetings

In an attempt to expand its enterprise offerings, Google released the Chromebox for Meetings in February 2014. The Chromebox for Meetings is a kit for conference rooms containing a Chromebox, a camera, a unit containing both a noise-cancelling microphone and speakers, and a remote control. It supports Google Hangouts meetings, Vidyo video conferences, and conference calls from UberConference. Several partners announced Chromebox for Meetings models with Google, and in 2016 Google announced an all-in-one Chromebase for Meetings for smaller meeting rooms.

Hardware

A Chromebook.
 
Laptops running Chrome OS are known collectively as "Chromebooks". The first was the CR-48, a reference hardware design that Google gave to testers and reviewers beginning in December 2010. Retail machines followed in May 2011. A year later, in May 2012, a desktop design marketed as a "Chromebox" was released by Samsung. In March 2015 a partnership with AOPEN was announced and the first commercial Chromebox was developed.

In early 2014, LG Electronics introduced the first device belonging to the new all-in-one form factor called "Chromebase". Chromebase devices are essentially Chromebox hardware inside a monitor with built-in camera, microphone and speakers. 

The Chromebit is an HDMI dongle running Chrome OS. When placed in an HDMI slot on a television set or computer monitor, the device turns that display into a personal computer. The device was announced in March 2015 and shipped that November.

Chrome OS supports dual-monitor setups, on devices with a video-out port.

Applications

Chrome OS running six different web browsers
 
Initially, Chrome OS was almost a pure web thin client operating system that relied primarily on servers to host web applications and related data storage. Google gradually began encouraging developers to create "packaged applications", and later, Chrome Apps. The latter employs HTML5, CSS, Adobe Shockwave, and JavaScript to provide a user experience closer to a native application.

In September 2014, Google launched App Runtime for Chrome (beta), which allowed certain ported Android applications to run on Chrome OS. Runtime was launched with four Android applications: Duolingo, Evernote, Sight Words, and Vine. In 2016, Google made the Google Play Store available for Chrome OS, making most Android apps available for supported Chrome OS devices.

Google announced in 2018 that Chrome OS would be getting support for desktop Linux apps. This capability was released to the stable channel with Chrome 69 in October 2018, but was still marked as beta.

Chrome Apps

Google has encouraged developers to build not just conventional Web applications for Chrome OS, but Chrome Apps (formerly known as Packaged apps). From a user perspective, Chrome Apps resemble conventional native applications: they can be launched outside of the Chrome browser, are offline by default, can manage multiple windows, and interact with other applications. Technologies employed include HTML5, JavaScript, and CSS.

Integrated media player, file manager

Google integrates a media player into both Chrome OS and the Chrome browser, enabling users to play back MP3s, view JPEGs, and handle other multimedia files while offline. It supports DRM videos.

Chrome OS also includes an integrated file manager, resembling those found on other operating systems, with the ability to display directories and the files they contain from both Google Drive and local storage, as well as to preview and manage file contents using a variety of Web applications, including Google Docs and Box. Since January 2015, Chrome OS can also integrate additional storage sources into the file manager, relying on installed extensions that use the File System Provider API.

Remote application access and virtual desktop access

In June 2010, Google software engineer Gary Kačmarčík wrote that Chrome OS will access remote applications through a technology unofficially called "Chromoting", which would resemble Microsoft's Remote Desktop Connection. The name has since been changed to "Chrome Remote Desktop", and is like "running an application via Remote Desktop Services or by first connecting to a host machine by using RDP or VNC". Initial roll-outs of Chrome OS laptops (Chromebooks) indicate an interest in enabling users to access virtual desktops.

Android applications

At Google I/O 2014, a proof of concept showing Android applications, including Flipboard, running on Chrome OS was presented. In September 2014, Google introduced a beta version of the App Runtime for Chrome (ARC), which allows selected Android applications to be used on Chrome OS, using a Native Client-based environment that provides the platforms necessary to run Android software. Android applications do not require any modifications to run on Chrome OS, but may be modified to better support a mouse and keyboard environment. At its introduction, Chrome OS support was only available for selected Android applications.

In 2016, Google introduced the ability to run Android apps on supported Chrome OS devices, with access to the entire Google Play Store. The previous Native Client-based solution was dropped in favor of a container containing Android's frameworks and dependencies (initially based on Android 6.0), which allows Android apps to have direct access to the Chrome OS platform, and allow the OS to interact with Android contracts such as sharing. Engineering director Zelidrag Hornung explained that ARC had been scrapped due to its limitations, including its incompatibility with the Android Native Development Toolkit (NDK), and that it was unable to pass Google's own compatibility test suite.

Linux Apps

Since 2013 it has been possible to run Linux applications in Chrome OS through the use of Crouton, a third-party set of scripts that allows access to a Linux distribution such as Ubuntu. However, in 2018 Google announced that desktop Linux apps were officially coming to Chrome OS. The main benefit claimed by Google of their official Linux application support is that it can run without enabling developer mode, keeping many of the security features of Chrome OS. It was noticed in the Chromium OS source code in early 2018. Early parts of Crostini were made available for the Google Pixelbook via the dev channel in February 2018 as part of Chrome OS version 66, and it was enabled by default via the beta channel for testing on a variety of chromebooks in August 2018 with version 69.

Architecture

Google's project for supporting Linux applications in Chrome OS is called Crostini, named for the Italian bread-based starter, and as a pun on Crouton. Crostini runs a virtual machine through a virtual machine monitor called crosvm, which uses Linux's built-in KVM virtualization tool. Although Crosvm supports multiple virtual machines, the one used for running Linux apps, Termina, contains a basic Chrome OS kernel and userland utilities, in which it runs containers based on Linux containers (specifically LXD).

Architecture

Chrome OS is built on top of the Linux kernel. Originally based on Ubuntu, its base was changed to Gentoo Linux in February 2010. In preliminary design documents for the Chromium OS open source project, Google described a three-tier architecture: firmware, browser and window manager, and system-level software and userland services.
  • The firmware contributes to fast boot time by not probing for hardware, such as floppy disk drives, that are no longer common on computers, especially netbooks. The firmware also contributes to security by verifying each step in the boot process and incorporating system recovery.
  • System-level software includes the Linux kernel that has been patched to improve boot performance. Userland software has been trimmed to essentials, with management by Upstart, which can launch services in parallel, re-spawn crashed jobs, and defer services in the interest of faster booting.
  • The window manager handles user interaction with multiple client windows much like other X window managers.

Security

In March 2010, Google software security engineer Will Drewry discussed Chrome OS security. Drewry described Chrome OS as a "hardened" operating system featuring auto-updating and sandbox features that will reduce malware exposure. He said that Chrome OS netbooks will be shipped with Trusted Platform Module (TPM), and include both a "trusted bootpath" and a physical switch under the battery compartment that actuates a developer mode. That mode drops some specialized security functions but increases developer flexibility. Drewry also emphasized that the open source nature of the operating system will contribute greatly to its security by allowing constant developer feedback.

At a December 2010 press conference, Google claimed that Chrome OS would be the most secure consumer operating system due in part to a verified boot ability, in which the initial boot code, stored in read-only memory, checks for system compromises.

Shell access

Chrome OS includes the Chrome Shell, or "crosh", which documents minimal functionality such as ping and SSH at crosh start-up. 

In developer mode, a full-featured bash shell (which is supposed to be used for development purposes) can be opened via VT-2, and is also accessible using the crosh command shell. To access full privileges in shell (e.g. sudo) a root password is requested. For some time the default was "chronos" in Chrome OS and "facepunch" in Chrome OS Vanilla and later the default was empty, and instructions on updating it were displayed at each login.

Open source

Chrome OS is partially developed under the open source Chromium OS project. As with other open source projects, developers can modify the code from Chromium OS and build their own versions, whereas Chrome OS code is only supported by Google and its partners and only runs on hardware designed for the purpose. Unlike Chromium OS, Chrome OS is automatically updated to the latest version.

Chrome OS on Windows

On Windows 8 exceptions allow the default desktop web browser to offer a variant that can run inside its full-screen "Metro" shell and access features such as the Share charm, without necessarily needing to be written with Windows Runtime. Chrome's "Windows 8 mode" was previously a tablet-optimized version of the standard Chrome interface. In October 2013, the mode was changed on Developer channel to offer a variant of the Chrome OS desktop.

Design

Early in the project, Google provided publicly many details of the Chrome OS's design goals and direction, although the company has not followed up with a technical description of the completed operating system.

User interface

Old Chrome-Chromium OS login screen
 
Design goals for Chrome OS's user interface included using minimal screen space by combining applications and standard Web pages into a single tab strip, rather than separating the two. Designers considered a reduced window management scheme that would operate only in full-screen mode. Secondary tasks would be handled with "panels": floating windows that dock to the bottom of the screen for tasks like chat and music players. Split screens were also under consideration for viewing two pieces of content side-by-side. Chrome OS would follow the Chrome browser's practice of leveraging HTML5's offline modes, background processing, and notifications. Designers proposed using search and pinned tabs as a way to quickly locate and access applications.

New window manager and graphics engine

On April 10, 2012, a new build of Chrome OS offered a choice between the original full-screen window interface and overlapping, re-sizable windows, such as found on Microsoft Windows and Apple's macOS. The feature was implemented through the Ash window manager, which runs atop the Aura hardware-accelerated graphics engine. The April 2012 upgrade also included the ability to display smaller, overlapping browser windows, each with its own translucent tabs, browser tabs that can be "torn" and dragged to new positions or merged with another tab strip, and a mouse-enabled shortcut list across the bottom of the screen. One icon on the task bar shows a list of installed applications and bookmarks. Writing in CNET, Stephen Shankland argued that with overlapping windows, "Google is anchoring itself into the past" as both iOS and Microsoft's Metro interface are largely or entirely full-screen. Even so, "Chrome OS already is different enough that it's best to preserve any familiarity that can be preserved".

Printing

Google Cloud Print is a Google service that helps any application on any device to print on supported printers. While the cloud provides virtually any connected device with information access, the task of "developing and maintaining print subsystems for every combination of hardware and operating system—from desktops to netbooks to mobile devices—simply isn't feasible." The cloud service requires installation of a piece of software called proxy, as part of the Chrome OS. The proxy registers the printer with the service, manages the print jobs, provides the printer driver functionality, and gives status alerts for each job.

In 2016, Google included "Native CUPS Support" in Chrome OS as an experimental feature that may eventually become an official feature. With CUPS support turned on, it becomes possible to use most USB printers even if they do not support Google Cloud Print.

Link handling

Chrome OS was designed with the intention of storing user documents and files on remote servers. Both Chrome OS and the Chrome browser may introduce difficulties to end users when handling specific file types offline; for example, when opening an image or document residing on a local storage device, it may be unclear whether and which specific Web application should be automatically opened for viewing, or the handling should be performed by a traditional application acting as a preview utility. Matthew Papakipos, Chrome OS engineering director, noted in 2010 that Windows developers have faced the same fundamental problem: "Quicktime is fighting with Windows Media Player, which is fighting with Chrome."

Release channels and updates

Chrome OS uses the same release system as Google Chrome: there are three distinct channels: Stable, Beta, and Developer preview (called the "Dev" channel). The stable channel is updated with features and fixes that have been thoroughly tested in the Beta channel, and the Beta channel is updated approximately once a month with stable and complete features from the Developer channel. New ideas get tested in the Developer channel, which can be very unstable at times. A fourth canary channel was confirmed to exist by Google Developer Francois Beaufort and hacker Kenny Strawn, by entering the Chrome OS shell in developer mode, typing the command shell to access the bash shell, and finally entering the command update_engine_client -channel canary-channel -update. It is possible to return to verified boot mode after entering the canary channel, but the channel updater disappears and the only way to return to another channel is using the "powerwash" factory reset.

Reception

At its debut, Chrome OS was viewed as a competitor to Microsoft, both directly to Microsoft Windows and indirectly the company's word processing and spreadsheet applications—the latter through Chrome OS's reliance on cloud computing. But Chrome OS engineering director Matthew Papakipos argued that the two operating systems would not fully overlap in functionality because Chrome OS is intended for netbooks, which lack the computational power to run a resource-intensive program like Adobe Photoshop.

Some observers claimed that other operating systems already filled the niche that Chrome OS was aiming for, with the added advantage of supporting native applications in addition to a browser. Tony Bradley of PC World wrote in November 2009: 

We can already do most, if not all, of what Chrome OS promises to deliver. Using a Windows 7 or Linux-based netbook, users can simply not install anything but a web browser and connect to the vast array of Google products and other web-based services and applications. Netbooks have been successful at capturing the low-end PC market, and they provide a web-centric computing experience today. I am not sure why we should get excited that a year from now we'll be able to do the same thing, but locked into doing it from the fourth-place web browser.

After this 2009 statement Chrome browser rose to become the number one browser used worldwide.

By 2016, Chromebooks had become the most popular computer in the US K–12 education market.

Relationship to Android

Google's offering of two open source operating systems, Android and Chrome OS, has drawn some criticism despite the similarity between this situation and that of Apple Inc's two operating systems, macOS and iOS. Steve Ballmer, Microsoft CEO at the time, accused Google of not being able to make up its mind. Steven Levy wrote that "the dissonance between the two systems was apparent" at Google I/O 2011. The event featured a daily press conference in which each team leader, Android's Andy Rubin and Chrome's Sundar Pichai, "unconvincingly tried to explain why the systems weren't competitive." Google co-founder Sergey Brin addressed the question by saying that owning two promising operating systems was "a problem that most companies would love to face". Brin suggested that the two operating systems "will likely converge over time." The speculation over convergence increased in March 2013 when Chrome OS chief Pichai replaced Rubin as the senior vice president in charge of Android, thereby putting Pichai in charge of both.

The relationship between Android and Chrome OS became more substantial at Google I/O 2014, where developers demonstrated native Android software running on Chrome OS through a Native Client based runtime. In October 2015, The Wall Street Journal reported that Chrome OS would be folded into Android so that a single OS would result by 2017. The resulting OS will be Android, but it will be expanded to run on laptops. Google responded that while the company has "been working on ways to bring together the best of both operating systems, there's no plan to phase out Chrome OS."

Unix

From Wikipedia, the free encyclopedia

Unix
Unix history-simple.svg
Evolution of Unix and Unix-like systems
DeveloperKen Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna at Bell Labs
Written inC and assembly language
OS familyUnix
Working stateCurrent
Source modelHistorically closed-source, while some Unix projects (including BSD family and illumos) are open-source
Initial releaseDevelopment started in 1969
First manual published internally in November 1971
Announced outside Bell Labs in October 1973
Available inEnglish
Kernel typeVaries; monolithic, microkernel, hybrid
Default user interfaceCommand-line interface and Graphical (X Window System)
LicenseVaries; some versions are proprietary, others are free/open-source software
Official websiteopengroup.org/unix

Unix (/ˈjnɪks/; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, development starting in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others.

Initially intended for use inside the Bell System, AT&T licensed Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including University of California, Berkeley (BSD), Microsoft (Xenix), IBM (AIX), and Sun Microsystems (Solaris). In the early 1990s, AT&T sold its rights in Unix to Novell, which then sold its Unix business to the Santa Cruz Operation (SCO) in 1995. The UNIX trademark passed to The Open Group, a neutral industry consortium, which allows the use of the mark for certified operating systems that comply with the Single UNIX Specification (SUS). As of 2014, the Unix version with the largest installed base is Apple's macOS.

Unix systems are characterized by a modular design that is sometimes called the "Unix philosophy". This concept entails that the operating system provides a set of simple tools that each performs a limited, well-defined function, with a unified filesystem (the Unix filesystem) as the main means of communication, and a shell scripting and command language (the Unix shell) to combine the tools to perform complex workflows. Unix distinguishes itself from its predecessors as the first portable operating system: almost the entire operating system is written in the C programming language, thus allowing Unix to reach numerous platforms.

Overview

Version 7 Unix, the Research Unix ancestor of all modern Unix systems
 
Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmers. The system grew larger as the operating system started spreading in academic circles, as users added their own tools to the system and shared them with colleagues.

At first, Unix was not designed to be portable or multi-tasking. Later, Unix gradually gained portability, multi-tasking and multi-user capabilities in a time-sharing configuration. Unix systems are characterized by various concepts: the use of plain text for storing data; a hierarchical file system; treating devices and certain types of inter-process communication (IPC) as files; and the use of a large number of software tools, small programs that can be strung together through a command-line interpreter using pipes, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are collectively known as the "Unix philosophy". Brian Kernighan and Rob Pike summarize this in The Unix Programming Environment as "the idea that the power of a system comes more from the relationships among programs than from the programs themselves".

In an era when a standard computer consisted of a hard disk for storage and a data terminal for input and output (I/O), the Unix file model worked quite well, as I/O was generally linear. In the 1980s, non-blocking I/O and the set of inter-process communication mechanisms were augmented with Unix domain sockets, shared memory, message queues, and semaphores, and network sockets were added to support communication with other hosts. As graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse.

By the early 1980s, users began seeing Unix as a potential universal operating system, suitable for computers of all sizes. The Unix environment and the client–server program model were essential elements in the development of the Internet and the reshaping of computing as centered in networks rather than in individual computers. 

Both Unix and the C programming language were developed by AT&T and distributed to government and academic institutions, which led to both being ported to a wider variety of machine families than any other operating system. 

Under Unix, the operating system consists of many libraries and utilities along with the master control program, the kernel. The kernel provides services to start and stop programs, handles the file system and other common "low-level" tasks that most programs share, and schedules access to avoid conflicts when programs try to access the same resource or device simultaneously. To mediate such access, the kernel has special rights, reflected in the division between user space and kernel space - although in microkernel implementations, like MINIX or Redox, functions such as network protocols may also run in user space.

History

Ken Thompson (sitting) and Dennis Ritchie working together at a PDP-11
 
The origins of Unix date back to the mid-1960s when the Massachusetts Institute of Technology, Bell Labs, and General Electric were developing Multics, a time-sharing operating system for the GE-645 mainframe computer. Multics featured several innovations, but also presented severe problems. Frustrated by the size and complexity of Multics, but not by its goals, individual researchers at Bell Labs started withdrawing from the project. The last to leave were Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna, who decided to reimplement their experiences in a new project of smaller scale. This new operating system was initially without organizational backing, and also without a name. 

The new operating system was a single-tasking system. In 1970, the group coined the name Unics for Uniplexed Information and Computing Service (pronounced "eunuchs"), as a pun on Multics, which stood for Multiplexed Information and Computer Services. Brian Kernighan takes credit for the idea, but adds that "no one can remember" the origin of the final spelling Unix. Dennis Ritchie, Doug McIlroy, and Peter G. Neumann also credit Kernighan.

The operating system was originally written in assembly language, but in 1973, Version 4 Unix was rewritten in C. Version 4 Unix, however, still had many PDP-11 dependent codes, and is not suitable for porting. The first port to other platform was made five years later (1978) for Interdata 8/32.

Bell Labs produced several versions of Unix that are collectively referred to as "Research Unix". In 1975, the first source license for UNIX was sold to Donald B. Gillies at the University of Illinois Department of Computer Science. UIUC graduate student Greg Chesson, who had worked on the UNIX kernel at Bell Labs, was instrumental in negotiating the terms of the license.

During the late 1970s and early 1980s, the influence of Unix in academic circles led to large-scale adoption of Unix (BSD and System V) by commercial startups, including Sequent, HP-UX, Solaris, AIX, and Xenix. In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4 (SVR4), which was subsequently adopted by many commercial Unix vendors. 

In the 1990s, Unix and Unix-like systems grew in popularity as BSD and Linux distributions were developed through collaboration by a worldwide network of programmers. In 2000, Apple released Darwin, also a Unix system, which became the core of the Mac OS X operating system, which was later renamed macOS.

Unix operating systems are widely used in modern servers, workstations, and mobile devices.

Standards

 
In the late 1980s, an open operating system standardization effort now known as POSIX provided a common baseline for all operating systems; IEEE based POSIX around the common structure of the major competing variants of the Unix system, publishing the first POSIX standard in 1988. In the early 1990s, a separate but very similar effort was started by an industry consortium, the Common Open Software Environment (COSE) initiative, which eventually became the Single UNIX Specification (SUS) administered by The Open Group. Starting in 1998, the Open Group and IEEE started the Austin Group, to provide a common definition of POSIX and the Single UNIX Specification, which, by 2008, had become the Open Group Base Specification. 

In 1999, in an effort towards compatibility, several Unix system vendors agreed on SVR4's Executable and Linkable Format (ELF) as the standard for binary and object code files. The common format allows substantial binary compatibility among Unix systems operating on the same CPU architecture. 

The Filesystem Hierarchy Standard was created to provide a reference directory layout for Unix-like operating systems, and has mainly been used in Linux.

Components

The Unix system is composed of several components that were originally packaged together. By including the development environment, libraries, documents and the portable, modifiable source code for all of these components, in addition to the kernel of an operating system, Unix was a self-contained software system. This was one of the key reasons it emerged as an important teaching and learning tool and has had such a broad influence.

The inclusion of these components did not make the system large – the original V7 UNIX distribution, consisting of copies of all of the compiled binaries plus all of the source code and documentation occupied less than 10 MB and arrived on a single nine-track magnetic tape. The printed documentation, typeset from the online sources, was contained in two volumes. 

The names and filesystem locations of the Unix components have changed substantially across the history of the system. Nonetheless, the V7 implementation is considered by many to have the canonical early structure:
  • Kernel – source code in /usr/sys, composed of several sub-components:
    • conf – configuration and machine-dependent parts, including boot code
    • dev – device drivers for control of hardware (and some pseudo-hardware)
    • sys – operating system "kernel", handling memory management, process scheduling, system calls, etc.
    • h – header files, defining key structures within the system and important system-specific invariables
  • Development environment – early versions of Unix contained a development environment sufficient to recreate the entire system from source code:
    • cc – C language compiler (first appeared in V3 Unix)
    • as – machine-language assembler for the machine
    • ld – linker, for combining object files
    • lib – object-code libraries (installed in /lib or /usr/lib). libc, the system library with C run-time support, was the primary library, but there have always been additional libraries for such things as mathematical functions (libm) or database access. V7 Unix introduced the first version of the modern "Standard I/O" library stdio as part of the system library. Later implementations increased the number of libraries significantly.
    • make – build manager (introduced in PWB/UNIX), for effectively automating the build process
    • include – header files for software development, defining standard interfaces and system invariants
    • Other languages – V7 Unix contained a Fortran-77 compiler, a programmable arbitrary-precision calculator (bc, dc), and the awk scripting language; later versions and implementations contain many other language compilers and toolsets. Early BSD releases included Pascal tools, and many modern Unix systems also include the GNU Compiler Collection as well as or instead of a proprietary compiler system.
    • Other tools – including an object-code archive manager (ar), symbol-table lister (nm), compiler-development tools (e.g. lex & yacc), and debugging tools.
  • Commands – Unix makes little distinction between commands (user-level programs) for system operation and maintenance (e.g. cron), commands of general utility (e.g. grep), and more general-purpose applications such as the text formatting and typesetting package. Nonetheless, some major categories are:
    • sh – the "shell" programmable command-line interpreter, the primary user interface on Unix before window systems appeared, and even afterward (within a "command window").
    • Utilities – the core toolkit of the Unix command set, including cp, ls, grep, find and many others. Subcategories include:
      • System utilities – administrative tools such as mkfs, fsck, and many others.
      • User utilities – environment management tools such as passwd, kill, and others.
    • Document formatting – Unix systems were used from the outset for document preparation and typesetting systems, and included many related programs such as nroff, troff, tbl, eqn, refer, and pic. Some modern Unix systems also include packages such as TeX and Ghostscript.
    • Graphics – the plot subsystem provided facilities for producing simple vector plots in a device-independent format, with device-specific interpreters to display such files. Modern Unix systems also generally include X11 as a standard windowing system and GUI, and many support OpenGL.
    • Communications – early Unix systems contained no inter-system communication, but did include the inter-user communication programs mail and write. V7 introduced the early inter-system communication system UUCP, and systems beginning with BSD release 4.1c included TCP/IP utilities.
  • Documentation – Unix was the first operating system to include all of its documentation online in machine-readable form. The documentation included:
    • man – manual pages for each command, library component, system call, header file, etc.
    • doc – longer documents detailing major subsystems, such as the C language and troff

Impact

Ken Thompson and Dennis Ritchie, principal developers of Research Unix
 
Photo from USENIX 1984, including Dennis Ritchie (center)
 
Plan 9 from Bell Labs extends Unix design principles and was developed as a successor to Unix.
 
The Unix system had significant impact on other operating systems. It achieved its reputation by its interactivity, by providing the software at a nominal fee for educational use, by running on inexpensive hardware, and by being easy to adapt and move to different machines. Unix was originally written in assembly language (which had been thought necessary for system implementations on early computers), but was soon rewritten in C, a high-level programming language. Although this followed the lead of Multics and Burroughs, it was Unix that popularized the idea. 

Unix had a drastically simplified file model compared to many contemporary operating systems: treating all kinds of files as simple byte arrays. The file system hierarchy contained machine services and devices (such as printers, terminals, or disk drives), providing a uniform interface, but at the expense of occasionally requiring additional mechanisms such as ioctl and mode flags to access features of the hardware that did not fit the simple "stream of bytes" model. The Plan 9 operating system pushed this model even further and eliminated the need for additional mechanisms. 

Unix also popularized the hierarchical file system with arbitrarily nested subdirectories, originally introduced by Multics. Other common operating systems of the era had ways to divide a storage device into multiple directories or sections, but they had a fixed number of levels, often only one level. Several major proprietary operating systems eventually added recursive subdirectory capabilities also patterned after Multics. DEC's RSX-11M's "group, user" hierarchy evolved into VMS directories, CP/M's volumes evolved into MS-DOS 2.0+ subdirectories, and HP's MPE group.account hierarchy and IBM's SSP and OS/400 library systems were folded into broader POSIX file systems. 

Making the command interpreter an ordinary user-level program, with additional commands provided as separate programs, was another Multics innovation popularized by Unix. The Unix shell used the same language for interactive commands as for scripting (shell scripts – there was no separate job control language like IBM's JCL). Since the shell and OS commands were "just another program", the user could choose (or even write) their own shell. New commands could be added without changing the shell itself. Unix's innovative command-line syntax for creating modular chains of producer-consumer processes (pipelines) made a powerful programming paradigm (coroutines) widely available. Many later command-line interpreters have been inspired by the Unix shell. 

A fundamental simplifying assumption of Unix was its focus on newline-delimited text for nearly all file formats. There were no "binary" editors in the original version of Unix – the entire system was configured using textual shell command scripts. The common denominator in the I/O system was the byte – unlike "record-based" file systems. The focus on text for representing nearly everything made Unix pipes especially useful, and encouraged the development of simple, general tools that could be easily combined to perform more complicated ad hoc tasks. The focus on text and bytes made the system far more scalable and portable than other systems. Over time, text-based applications have also proven popular in application areas, such as printing languages (PostScript, ODF), and at the application layer of the Internet protocols, e.g., FTP, SMTP, HTTP, SOAP, and SIP

Unix popularized a syntax for regular expressions that found widespread use. The Unix programming interface became the basis for a widely implemented operating system interface standard (POSIX, see above). The C programming language soon spread beyond Unix, and is now ubiquitous in systems and applications programming. 

Early Unix developers were important in bringing the concepts of modularity and reusability into software engineering practice, spawning a "software tools" movement. Over time, the leading developers of Unix (and programs that ran on it) established a set of cultural norms for developing software, norms which became as important and influential as the technology of Unix itself; this has been termed the Unix philosophy

The TCP/IP networking protocols were quickly implemented on the Unix versions widely used on relatively inexpensive computers, which contributed to the Internet explosion of worldwide real-time connectivity, and which formed the basis for implementations on many other platforms. 

The Unix policy of extensive on-line documentation and (for many years) ready access to all system source code raised programmer expectations, and contributed to the 1983 launch of the free software movement.

Free Unix and Unix-like variants

Console screenshots of Debian (top, a popular Linux distribution) and FreeBSD (bottom, a popular Unix-like operating system)
 
In 1983, Richard Stallman announced the GNU (short for "GNU's Not Unix") project, an ambitious effort to create a free software Unix-like system; "free" in the sense that everyone who received a copy would be free to use, study, modify, and redistribute it. The GNU project's own kernel development project, GNU Hurd, had not yet produced a working kernel, but in 1991 Linus Torvalds released the Linux kernel as free software under the GNU General Public License. In addition to their use in the Linux operating system, many GNU packages – such as the GNU Compiler Collection (and the rest of the GNU toolchain), the GNU C library and the GNU core utilities – have gone on to play central roles in other free Unix systems as well. 

Linux distributions, consisting of the Linux kernel and large collections of compatible software have become popular both with individual users and in business. Popular distributions include Red Hat Enterprise Linux, Fedora, SUSE Linux Enterprise, openSUSE, Debian GNU/Linux, Ubuntu, Linux Mint, Mandriva Linux, Slackware Linux, Arch Linux and Gentoo.

A free derivative of BSD Unix, 386BSD, was released in 1992 and led to the NetBSD and FreeBSD projects. With the 1994 settlement of a lawsuit brought against the University of California and Berkeley Software Design Inc. (USL v. BSDi) by Unix Systems Laboratories, it was clarified that Berkeley had the right to distribute BSD Unix for free, if it so desired. Since then, BSD Unix has been developed in several different product branches, including OpenBSD and DragonFly BSD

Linux and BSD are increasingly filling the market needs traditionally served by proprietary Unix operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. Because of the modular design of the Unix model, sharing components is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and some systems also include GNU utilities in their distributions. 

In a 1999 interview, Dennis Ritchie voiced his opinion that Linux and BSD operating systems are a continuation of the basis of the Unix design, and are derivatives of Unix:
I think the Linux phenomenon is quite delightful, because it draws so strongly on the basis that Unix provided. Linux seems to be the among the healthiest of the direct Unix derivatives, though there are also the various BSD systems as well as the more official offerings from the workstation and mainframe manufacturers.
In the same interview, he states that he views both Unix and Linux as "the continuation of ideas that were started by Ken and me and many others, many years ago."

OpenSolaris was the open-source counterpart to Solaris developed by Sun Microsystems, which included a CDDL-licensed kernel and a primarily GNU userland. However, Oracle discontinued the project upon their acquisition of Sun, which prompted a group of former Sun employees and members of the OpenSolaris community to fork OpenSolaris into the illumos kernel. As of 2014, illumos remains the only active open-source System V derivative.

ARPANET

In May 1975, RFC 681 described the development of Network Unix by the Center for Advanced Computation at the University of Illinois. The system was said to "present several interesting capabilities as an ARPANET mini-host". At the time Unix required a license from Bell Laboratories that at $20,000(US) was very expensive for non-university users, while an educational license cost just $150. It was noted that Bell was "open to suggestions" for an ARPANET-wide license. 

Specific features found beneficial were the local processing facilities, compilers, editors, a document preparation system, efficient file system and access control, mountable and unmountable volumes, unified treatment of peripherals as special files, integration of the network control program (NCP) within the Unix file system, treatment of network connections as special files that can be accessed through standard Unix I/O calls, closing of all files on program exit, and the decision to be "desirable to minimize the amount of code added to the basic Unix kernel".

Branding

HP9000 workstation running HP-UX, a certified Unix operating system
 
In October 1993, Novell, the company that owned the rights to the Unix System V source at the time, transferred the trademarks of Unix to the X/Open Company (now The Open Group), and in 1995 sold the related business operations to Santa Cruz Operation (SCO). Whether Novell also sold the copyrights to the actual software was the subject of a 2006 federal lawsuit, SCO v. Novell, which Novell won. The case was appealed, but on August 30, 2011, the United States Court of Appeals for the Tenth Circuit affirmed the trial decisions, closing the case. Unix vendor SCO Group Inc. accused Novell of slander of title

The present owner of the trademark UNIX is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX" (others are called "Unix-like"). 

By decree of The Open Group, the term "UNIX" refers more to a class of operating systems than to a specific implementation of an operating system; those operating systems which meet The Open Group's Single UNIX Specification should be able to bear the UNIX 98 or UNIX 03 trademarks today, after the operating system's vendor pays a substantial certification fee and annual trademark royalties to The Open Group. Systems licensed to use the UNIX trademark include AIX, HP-UX, Inspur K-UX, IRIX, Solaris, Tru64 UNIX (formerly "Digital UNIX", or OSF/1), macOS, and a part of z/OS. Notably, Inspur K-UX is a Linux distribution certified as UNIX 03 compliant.

Sometimes a representation like Un*x, *NIX, or *N?X is used to indicate all operating systems similar to Unix. This comes from the use of the asterisk (*) and the question mark characters as wildcard indicators in many utilities. This notation is also used to describe other Unix-like systems that have not met the requirements for UNIX branding from the Open Group.

The Open Group requests that UNIX is always used as an adjective followed by a generic term such as system to help avoid the creation of a genericized trademark

Unix was the original formatting, but the usage of UNIX remains widespread because it was once typeset in small caps (Unix). According to Dennis Ritchie, when presenting the original Unix paper to the third Operating Systems Symposium of the American Association for Computing Machinery (ACM), "we had a new typesetter and troff had just been invented and we were intoxicated by being able to produce small caps." Many of the operating system's predecessors and contemporaries used all-uppercase lettering, so many people wrote the name in upper case due to force of habit. It is not an acronym.

Trademark names can be registered by different entities in different countries and trademark laws in some countries allow the same trademark name to be controlled by two different entities if each entity uses the trademark in easily distinguishable categories. The result is that Unix has been used as a brand name for various products including book shelves, ink pens, bottled glue, diapers, hair driers and food containers.

Several plural forms of Unix are used casually to refer to multiple brands of Unix and Unix-like systems. Most common is the conventional Unixes, but Unices, treating Unix as a Latin noun of the third declension, is also popular. The pseudo-Anglo-Saxon plural form Unixen is not common, although occasionally seen. Sun Microsystems, developer of the Solaris variant, has asserted that the term Unix is itself plural, referencing its many implementations.

Lie point symmetry

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