Text-based user interface
Text-based user interface called textual user interface or terminal user interface, is a retronym coined sometime after the invention of graphical user interfaces. TUIs display computer graphics in text mode. An advanced TUI may, like GUIs, accept mouse and other inputs. From text application's point of view, a text screen can belong to one of three types: A genuine text mode display, controlled by a video adapter or the central processor itself; this is a normal condition for a locally running application on various types of personal computers and mobile devices. If not deterred by the operating system, a smart program may exploit the full power of a hardware text mode. A text mode emulator. Examples are win32 console for Microsoft Windows; this supports programs which expect a real text mode display, but may run slower. Certain functions of an advanced text mode, such as an own font uploading certainly become unavailable. A remote text terminal; the communication capabilities become reduced to a serial line or its emulation with few ioctls as an out-of-band channel in such cases as Telnet and Secure Shell.
This is the worst case, because software restrictions hinder the use of capabilities of a remote display device. Under Linux and other Unix-like systems, a program accommodates to any of the three cases because the same interface controls the display and keyboard. Specialized programming libraries help to output the text in a way appropriate to the given display device and interface to it. See below for a comparison to Windows. American National Standards Institute standard ANSI X3.64 defines a standard set of escape sequences that can be used to drive terminals to create TUIs. Escape sequences may be supported for all three cases mentioned in the above section, allowing random cursor movements and color changes. However, not all terminals follow this standard, many non-compatible but functionally equivalent sequences exist. On IBM Personal Computers and compatibles, the Basic Input Output System and DOS system calls provide a way to write text on the screen, the ANSI. SYS driver could process standard ANSI escape sequences.
However, programmers soon learned that writing data directly to the screen buffer was far faster and simpler to program, less error-prone. This change in programming methods resulted in many DOS TUI programs; the win32 console environment is notorious for its emulation of certain EGA/VGA text mode features random access to the text buffer if the application runs in a window. On the other hand, programs running under Windows have much less control of the display and keyboard than Linux and DOS programs can have, because of aforementioned win32 console layer. Most those programs used a blue background for the main screen, with white or yellow characters, although they had user color customization, they used box-drawing characters in IBM's code page 437. The interface became influenced by graphical user interfaces, adding pull-down menus, overlapping windows, dialog boxes and GUI widgets operated by mnemonics or keyboard shortcuts. Soon mouse input was added – either at text resolution as a simple colored box or at graphical resolution thanks to the ability of the Enhanced Graphics Adapter and Video Graphics Array display adapters to redefine the text character shapes by software – providing additional functions.
Some notable programs of this kind were Microsoft Word, DOS Shell, WordPerfect, Norton Commander, Turbo Vision based Borland Turbo Pascal and Turbo C, Lotus 1-2-3 and many others. Some of these interfaces survived during the Microsoft Windows 3.1x period in the early 1990s. For example, the Microsoft C 6.0 compiler, used to write true GUI programs under 16-bit Windows, still has its own TUI. Since its start, Microsoft Windows includes a console to display DOS software. Versions added the Win32 console as a native interface for command-line interface and TUI programs; the console opens in window mode, but it can be switched to full, true text mode screen and vice versa by pressing the Alt and Enter keys together. Full-screen mode is not available in Windows Vista and but may be used with some workarounds. In Unix-like operating systems, TUIs are constructed using the terminal control library curses, or ncurses, a compatible library; the advent of the curses library with Berkeley Unix created a portable and stable API for which to write TUIs.
The ability to talk to various text terminal types using the same interfaces led to more widespread use of "visual" Unix programs, which occupied the entire terminal screen instead of using a simple line interface. This can be seen in text editors such as vi, mail clients such as pine or mutt, system management tools such as SMIT, SAM, FreeBSD's Sysinstall and web browsers such as lynx; some applications, such as w3m, older versions of pine and vi use the less-able termcap library, performing many of the functions associated with curses within the application. In addition, the rise in popularity of Linux brought many former DOS users to a Unix-like platform, which has fostered a DOS influence in many TUIs; the program minicom, for example, is modeled after the popular DOS program Telix. Some other TUI programs, such as the Twin desktop, were ported over; the Linux kernel supports virtual consoles accessed through a Ctrl-Alt-F key combination. Up to 64 consoles may be
Linux is a family of free and open-source software operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is packaged in a Linux distribution. Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy. Popular Linux distributions include Debian and Ubuntu. Commercial distributions include SUSE Linux Enterprise Server. Desktop Linux distributions include a windowing system such as X11 or Wayland, a desktop environment such as GNOME or KDE Plasma. Distributions intended for servers may omit graphics altogether, include a solution stack such as LAMP; because Linux is redistributable, anyone may create a distribution for any purpose. Linux was developed for personal computers based on the Intel x86 architecture, but has since been ported to more platforms than any other operating system.
Linux is the leading operating system on servers and other big iron systems such as mainframe computers, the only OS used on TOP500 supercomputers. It is used by around 2.3 percent of desktop computers. The Chromebook, which runs the Linux kernel-based Chrome OS, dominates the US K–12 education market and represents nearly 20 percent of sub-$300 notebook sales in the US. Linux runs on embedded systems, i.e. devices whose operating system is built into the firmware and is tailored to the system. This includes routers, automation controls, digital video recorders, video game consoles, smartwatches. Many smartphones and tablet computers run other Linux derivatives; because of the dominance of Android on smartphones, Linux has the largest installed base of all general-purpose operating systems. Linux is one of the most prominent examples of open-source software collaboration; the source code may be used and distributed—commercially or non-commercially—by anyone under the terms of its respective licenses, such as the GNU General Public License.
The Unix operating system was conceived and implemented in 1969, at AT&T's Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas McIlroy, Joe Ossanna. First released in 1971, Unix was written in assembly language, as was common practice at the time. In a key pioneering approach in 1973, it was rewritten in the C programming language by Dennis Ritchie; the availability of a high-level language implementation of Unix made its porting to different computer platforms easier. Due to an earlier antitrust case forbidding it from entering the computer business, AT&T was required to license the operating system's source code to anyone who asked; as a result, Unix grew and became adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs; the GNU Project, started in 1983 by Richard Stallman, had the goal of creating a "complete Unix-compatible software system" composed of free software. Work began in 1984. In 1985, Stallman started the Free Software Foundation and wrote the GNU General Public License in 1989.
By the early 1990s, many of the programs required in an operating system were completed, although low-level elements such as device drivers and the kernel, called GNU/Hurd, were stalled and incomplete. Linus Torvalds has stated that if the GNU kernel had been available at the time, he would not have decided to write his own. Although not released until 1992, due to legal complications, development of 386BSD, from which NetBSD, OpenBSD and FreeBSD descended, predated that of Linux. Torvalds has stated that if 386BSD had been available at the time, he would not have created Linux. MINIX was created by Andrew S. Tanenbaum, a computer science professor, released in 1987 as a minimal Unix-like operating system targeted at students and others who wanted to learn the operating system principles. Although the complete source code of MINIX was available, the licensing terms prevented it from being free software until the licensing changed in April 2000. In 1991, while attending the University of Helsinki, Torvalds became curious about operating systems.
Frustrated by the licensing of MINIX, which at the time limited it to educational use only, he began to work on his own operating system kernel, which became the Linux kernel. Torvalds began the development of the Linux kernel on MINIX and applications written for MINIX were used on Linux. Linux matured and further Linux kernel development took place on Linux systems. GNU applications replaced all MINIX components, because it was advantageous to use the available code from the GNU Project with the fledgling operating system. Torvalds initiated a switch from his original license, which prohibited commercial redistribution, to the GNU GPL. Developers worked to integrate GNU components with the Linux kernel, making a functional and free operating system. Linus Torvalds had wanted to call his invention "Freax", a portmant
An operating system is system software that manages computer hardware and software resources and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is executed directly by the hardware and makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers; the dominant desktop operating system is Microsoft Windows with a market share of around 82.74%. MacOS by Apple Inc. is in second place, the varieties of Linux are collectively in third place. In the mobile sector, use in 2017 is up to 70% of Google's Android and according to third quarter 2016 data, Android on smartphones is dominant with 87.5 percent and a growth rate 10.3 percent per year, followed by Apple's iOS with 12.1 percent and a per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent.
Linux distributions are dominant in supercomputing sectors. Other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can only run one program at a time, while a multi-tasking operating system allows more than one program to be running in concurrency; this is achieved by time-sharing, where the available processor time is divided between multiple processes. These processes are each interrupted in time slices by a task-scheduling subsystem of the operating system. Multi-tasking may be characterized in co-operative types. In preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Unix-like operating systems, such as Solaris and Linux—as well as non-Unix-like, such as AmigaOS—support preemptive multitasking. Cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking.
32-bit versions of both Windows NT and Win9x, used preemptive multi-tasking. Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users, the system permits multiple users to interact with the system at the same time. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources to multiple users. A distributed operating system manages a group of distinct computers and makes them appear to be a single computer; the development of networked computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine; when computers in a group work in cooperation, they form a distributed system.
In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system saving it as a tool for multiple running virtual machines. The technique is used both in virtualization and cloud computing management, is common in large server warehouses. Embedded operating systems are designed to be used in embedded computer systems, they are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources, they are compact and efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is an operating system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavior is achieved. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts.
A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments. Early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could automatically run different programs in succession to speed up processing. Operating systems did not exist in their more complex forms until the early 1960s. Hardware features were added, that enabled use of runtime libraries and parallel processing; when personal computers became popular in the 1980s, operating systems were made for them similar in concept to those used on larger computers. In the 1940s, the earliest electronic digital systems had no operating systems.
Electronic systems of this time were programmed on rows of mechanical switches or by jumper wires on plug boards. These were special-purpose systems that, for example, generated ballistics tables for the military or controlled the pri
GNU nano is a text editor for Unix-like computing systems or operating environments using a command line interface. It emulates the Pico text editor, part of the Pine email client, provides additional functionality. Unlike Pico, nano is licensed under the GNU General Public License. Released as free software by Chris Allegretta in 1999, nano became part of the GNU Project in 2001. GNU nano was first created in 1999 by Chris Allegretta, his motivation was to create a free software replacement for Pico, not distributed under a free software license. The name was changed to nano on 10 January 2000 to avoid a naming conflict with the existing Unix utility tip; the name comes from the system of SI prefixes. In February 2001, nano became a part of the GNU Project. GNU nano implements several features that Pico lacks, including syntax highlighting, line numbers, regular expression search and replace, line-by-line scrolling, multiple buffers, indenting groups of lines, rebindable key support, the undoing and redoing of edit changes.
On 11 August 2003, Chris Allegretta handed the source code maintenance of nano to David Lawrence Ramsey. On 20 December 2007, Ramsey stepped down as nano's maintainer. On version 2.6.0 in June 2016, the current principal developer and the other active members of the nano project decided in consensus to leave the GNU project, because of their objections over the Free Software Foundation's copyright assignment policy, their belief that decentralized copyright ownership does not impede the ability to enforce the GNU General Public License. The step was acknowledged by Debian and Arch Linux, while the GNU project resisted the move and called it a "fork". On 19 August 2016, Chris Allegretta announced the return of the project to the GNU family, following concessions from GNU on copyright assignment for Nano which happened when version 2.7.0 was released in September 2016. GNU nano, like Pico, is keyboard-oriented, controlled with control keys. For example, Ctrl+O saves the current file. GNU nano puts a two-line "shortcut bar" at the bottom of the screen, listing many of the commands available in the current context.
For a complete list, Ctrl+G gets the help screen. Unlike Pico, nano uses meta keys to toggle its behavior. For example, Meta + S toggles smooth scrolling mode off. All features that can be selected from the command line can be dynamically toggled. On keyboards without the meta key it is mapped to the escape key, such that in order to simulate, Meta+S one has to press the Esc key release it, press the S key. GNU nano can use pointer devices, such as a mouse, to activate functions that are on the shortcut bar, as well as position the cursor. Comparison of text editors List of text editors List of Unix commands Pico Official website
World Wide Web
The World Wide Web known as the Web, is an information space where documents and other web resources are identified by Uniform Resource Locators, which may be interlinked by hypertext, are accessible over the Internet. The resources of the WWW may be accessed by users by a software application called a web browser. English scientist Tim Berners-Lee invented the World Wide Web in 1989, he wrote the first web browser in 1990 while employed at CERN near Switzerland. The browser was released outside CERN in 1991, first to other research institutions starting in January 1991 and to the general public in August 1991; the World Wide Web has been central to the development of the Information Age and is the primary tool billions of people use to interact on the Internet. Web resources may be any type of downloaded media, but web pages are hypertext media that have been formatted in Hypertext Markup Language; such formatting allows for embedded hyperlinks that contain URLs and permit users to navigate to other web resources.
In addition to text, web pages may contain images, video and software components that are rendered in the user's web browser as coherent pages of multimedia content. Multiple web resources with a common theme, a common domain name, or both, make up a website. Websites are stored in computers that are running a program called a web server that responds to requests made over the Internet from web browsers running on a user's computer. Website content can be provided by a publisher, or interactively where users contribute content or the content depends upon the users or their actions. Websites may be provided for a myriad of informative, commercial, governmental, or non-governmental reasons. Tim Berners-Lee's vision of a global hyperlinked information system became a possibility by the second half of the 1980s. By 1985, the global Internet began to proliferate in Europe and the Domain Name System came into being. In 1988 the first direct IP connection between Europe and North America was made and Berners-Lee began to discuss the possibility of a web-like system at CERN.
While working at CERN, Berners-Lee became frustrated with the inefficiencies and difficulties posed by finding information stored on different computers. On March 12, 1989, he submitted a memorandum, titled "Information Management: A Proposal", to the management at CERN for a system called "Mesh" that referenced ENQUIRE, a database and software project he had built in 1980, which used the term "web" and described a more elaborate information management system based on links embedded as text: "Imagine the references in this document all being associated with the network address of the thing to which they referred, so that while reading this document, you could skip to them with a click of the mouse." Such a system, he explained, could be referred to using one of the existing meanings of the word hypertext, a term that he says was coined in the 1950s. There is no reason, the proposal continues, why such hypertext links could not encompass multimedia documents including graphics and video, so that Berners-Lee goes on to use the term hypermedia.
With help from his colleague and fellow hypertext enthusiast Robert Cailliau he published a more formal proposal on 12 November 1990 to build a "Hypertext project" called "WorldWideWeb" as a "web" of "hypertext documents" to be viewed by "browsers" using a client–server architecture. At this point HTML and HTTP had been in development for about two months and the first Web server was about a month from completing its first successful test; this proposal estimated that a read-only web would be developed within three months and that it would take six months to achieve "the creation of new links and new material by readers, authorship becomes universal" as well as "the automatic notification of a reader when new material of interest to him/her has become available". While the read-only goal was met, accessible authorship of web content took longer to mature, with the wiki concept, WebDAV, Web 2.0 and RSS/Atom. The proposal was modelled after the SGML reader Dynatext by Electronic Book Technology, a spin-off from the Institute for Research in Information and Scholarship at Brown University.
The Dynatext system, licensed by CERN, was a key player in the extension of SGML ISO 8879:1986 to Hypermedia within HyTime, but it was considered too expensive and had an inappropriate licensing policy for use in the general high energy physics community, namely a fee for each document and each document alteration. A NeXT Computer was used by Berners-Lee as the world's first web server and to write the first web browser, WorldWideWeb, in 1990. By Christmas 1990, Berners-Lee had built all the tools necessary for a working Web: the first web browser and the first web server; the first web site, which described the project itself, was published on 20 December 1990. The first web page may be lost, but Paul Jones of UNC-Chapel Hill in North Carolina announced in May 2013 that Berners-Lee gave him what he says is the oldest known web page during a 1991 visit to UNC. Jones stored it on his NeXT computer. On 6 August 1991, Berners-Lee published a short summary of the World Wide Web project on the newsgroup alt.hypertext.
This date is sometimes confused with the public availability of the first web servers, which had occurred months earlier. As another example of such confusion, several news media reported that the first photo on the Web was published by Berners-Lee in 1992, an image of the CERN house band Les Horribles Cernettes taken by Silvano de Gennaro.
Free and open-source software
Free and open-source software is software that can be classified as both free software and open-source software. That is, anyone is licensed to use, copy and change the software in any way, the source code is shared so that people are encouraged to voluntarily improve the design of the software; this is in contrast to proprietary software, where the software is under restrictive copyright licensing and the source code is hidden from the users. FOSS maintains the software user's civil liberty rights. Other benefits of using FOSS can include decreased software costs, increased security and stability, protecting privacy and giving users more control over their own hardware. Free and open-source operating systems such as Linux and descendants of BSD are utilized today, powering millions of servers, desktops and other devices. Free-software licenses and open-source licenses are used by many software packages; the free-software movement and the open-source software movement are online social movements behind widespread production and adoption of FOSS.
"Free and open-source software" is an umbrella term for software, considered both Free software and open-source software. FOSS allows the user to inspect the source code and provides a high level of control of the software's functions compared to proprietary software; the term "free software" does not refer to the monetary cost of the software at all, but rather whether the license maintains the software user's civil liberties. There are a number of related terms and abbreviations for free and open-source software, or free/libre and open-source software. Although there is a complete overlap between free-software licenses and open-source-software licenses, there is a strong philosophical disagreement between the advocates of these two positions; the terminology of FOSS or "Free and Open-source software" was created to be a neutral on these philosophical disagreements between the FSF and OSI and have a single unified term that could refer to both concepts. As the Free Software Foundation explains the philosophical difference between free software and open-source software: "The two terms describe the same category of software, but they stand for views based on fundamentally different values.
Open-source is a development methodology. For the free-software movement, free software is an ethical imperative, essential respect for the users' freedom. By contrast, the philosophy of open-source considers issues in terms of how to make software “better”—in a practical sense only." In parallel to this the Open Source Initiative considers many free-software licenses to be open source. These include the latest versions of the FSF's three main licenses: the GPL, the Lesser General Public License, the GNU Affero General Public License. Richard Stallman's Free Software Definition, adopted by the Free Software Foundation, defines free software as a matter of liberty not price, it upholds the Four Essential Freedoms; the earliest-known publication of the definition of his free-software idea was in the February 1986 edition of the FSF's now-discontinued GNU's Bulletin publication. The canonical source for the document is in the philosophy section of the GNU Project website; as of August 2017, it is published there in 40 languages.
To meet the definition of "free software", the FSF requires the software's licensing rights what the FSF respect the civil liberties / human rights of what the FSF calls the software user's "Four Essential Freedoms". The freedom to run the program as you wish, for any purpose; the freedom to study how the program works, change it so it does your computing as you wish. Access to the source code is a precondition for this; the freedom to redistribute copies. The freedom to distribute copies of your modified versions to others. By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this; the open-source-software definition is used by the Open Source Initiative to determine whether a software license qualifies for the organization's insignia for Open-source software. The definition was based on the Debian Free Software Guidelines and adapted by Bruce Perens. Perens did not base his writing on the Four Essential Freedoms of free software from the Free Software Foundation, which were only available on the web.
Perens subsequently stated that he felt Eric Raymond's promotion of Open-source unfairly overshadowed the Free Software Foundation's efforts and reaffirmed his support for Free software. In the following 2000s, he spoke about open source again. In the 1950s through the 1980s, it was common for computer users to have the source code for all programs they used, the permission and ability to modify it for their own use. Software, including source code, was shared by individuals who used computers as public domain software. Most companies had a business model based on hardware sales, provided or bundled software with hardware, free of charge. By the late 1960s, the prevailing business model around software was changing. A growing and evolving software industry was competing with the hardware manufacturer's bundled software products. Leased machines required software support while providing n
Richard Matthew Stallman known by his initials, RMS, is an American free software movement activist and programmer. He campaigns for software to be distributed in a manner such that its users receive the freedoms to use, study and modify that software. Software that ensures these freedoms is termed free software. Stallman launched the GNU Project, founded the Free Software Foundation, developed the GNU Compiler Collection and GNU Emacs, wrote the GNU General Public License. Stallman launched the GNU Project in September 1983 to create a Unix-like computer operating system composed of free software. With this, he launched the free software movement, he has been the GNU project's lead architect and organizer, developed a number of pieces of used GNU software including, among others, the GNU Compiler Collection, the GNU Debugger and the GNU Emacs text editor. In October 1985 he founded the Free Software Foundation. Stallman pioneered the concept of copyleft, which uses the principles of copyright law to preserve the right to use and distribute free software, is the main author of free software licenses which describe those terms, most notably the GNU General Public License, the most used free software license.
In 1989, he co-founded the League for Programming Freedom. Since the mid-1990s, Stallman had spent most of his time advocating for free software, as well as campaigning against software patents, digital rights management, other legal and technical systems which he sees as taking away users' freedoms; this has included software license agreements, non-disclosure agreements, activation keys, copy restriction, proprietary formats and binary executables without source code. Stallman was born March 16, 1953 in New York City, to a family of Jewish heritage, though Stallman is an atheist, his parents are Alice Lippman, a school teacher, Daniel Stallman, a printing press broker. Stallman had a difficult relationship with his parents, as his father had a drinking habit and verbally abused his stepmother, he came to describe his parents as "tyrants". He was interested in computers at a young age. From 1967 to 1969, Stallman attended a Columbia University Saturday program for high school students. Stallman was a volunteer laboratory assistant in the biology department at Rockefeller University.
Although he was interested in mathematics and physics, his teaching professor at Rockefeller thought he showed promise as a biologist. His first experience with actual computers was at the IBM New York Scientific Center when he was in high school, he was hired for the summer in 1970, following his senior year of high school, to write a numerical analysis program in Fortran. He completed the task after a couple of weeks and spent the rest of the summer writing a text editor in APL and a preprocessor for the PL/I programming language on the IBM System/360; as a first-year student at Harvard University in fall 1970, Stallman was known for his strong performance in Math 55. He was happy: "For the first time in my life, I felt I had found a home at Harvard."In 1971, near the end of his first year at Harvard, he became a programmer at the MIT Artificial Intelligence Laboratory, became a regular in the hacker community, where he was known by his initials, RMS. Stallman received a bachelor's degree in physics from Harvard in 1974.
Stallman considered staying on at Harvard, but instead he decided to enroll as a graduate student at the Massachusetts Institute of Technology. He pursued a doctorate in physics for one year, but left that program to focus on his programming at the MIT AI Laboratory. While working as a research assistant at MIT under Gerry Sussman, Stallman published a paper in 1977 on an AI truth maintenance system, called dependency-directed backtracking; this paper was an early work on the problem of intelligent backtracking in constraint satisfaction problems. As of 2009, the technique Stallman and Sussman introduced is still the most general and powerful form of intelligent backtracking; the technique of constraint recording, wherein partial results of a search are recorded for reuse, was introduced in this paper. As a hacker in MIT's AI laboratory, Stallman worked on software projects such as TECO, Emacs for ITS, the Lisp machine operating system, he would become an ardent critic of restricted computer access in the lab, which at that time was funded by the Defense Advanced Research Projects Agency.
When MIT's Laboratory for Computer Science installed a password control system in 1977, Stallman found a way to decrypt the passwords and sent users messages containing their decoded password, with a suggestion to change it to the empty string instead, to re-enable anonymous access to the systems. Around 20 percent of the users followed his advice at the time, although passwords prevailed. Stallman boasted of the success of his campaign for many years afterward. In the late 1970s and early 1980s, the hacker culture that Stallman thrived on began to fragment. To prevent software from being used on their competitors' computers, most manufacturers stopped distributing source code and began using copyright and restrictive software licenses to limit or prohibit copying and redistribution. Such