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120-412: In order to ensure that the entire software of a computer grants its users all freedom rights (use, share, study, modify), even the most fundamental and important part, the operating system (including all its numerous utility programs) needed to be free software. Stallman decided to call this operating system GNU (a recursive acronym meaning " GNU's not Unix! "), basing its design on that of Unix ,

240-453: A linker . The GNU system required its own C compiler and tools to be free software, so these also had to be developed. By June 1987, the project had accumulated and developed free software for an assembler , an almost finished portable optimizing C compiler ( GCC ), an editor ( GNU Emacs ), and various Unix utilities (such as ls , grep , awk , make and ld ). They had an initial kernel that needed more updates. Once

360-428: A system call to perform a block I/O write operation, then the system call might execute the following instructions: While the writing takes place, the operating system will context switch to other processes as normal. When the device finishes writing, the device will interrupt the currently running process by asserting an interrupt request . The device will also place an integer onto the data bus. Upon accepting

480-500: A combination of GNU packages with a Linux-libre kernel (a modified Linux kernel that removes binary blobs, obfuscated code, and portions of code under proprietary licenses) and consist only of free software (eschewing proprietary software entirely). Distributions that have adopted the GNU FSDG include Dragora GNU/Linux-Libre , GNU Guix System , Hyperbola GNU/Linux-libre , Parabola GNU/Linux-libre , Trisquel GNU/Linux , PureOS , and

600-645: A computer even if they are not compatible with the base operating system. A library operating system (libOS) 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 a single application and configuration code to construct a unikernel : a specialized (only the absolute necessary pieces of code are extracted from libraries and bound together ), single address space , machine image that can be deployed to cloud or embedded environments. The operating system code and application code are not executed in separated protection domains (there

720-453: A copyleft-licensed work are expected to reciprocate the author's action of copyleft-licensing the software by also copyleft-licensing any derivatives they might have made. Because of this requirement, copyleft licenses have also been described as "viral" due to their self-perpetuating terms. In addition to restrictions on copying, copyleft licenses address other possible impediments. They ensure that rights cannot be later revoked , and require

840-585: A development of MULTICS for a single user. Because UNIX's source code was available, it became the basis of other, incompatible operating systems, of which the most successful were AT&T 's System V and the University of California 's Berkeley Software Distribution (BSD). To increase compatibility, the IEEE released the POSIX standard for operating system application programming interfaces (APIs), which

960-527: A divisive issue in the ideological strife between the Open Source Initiative and the free software movement . However, there is evidence that copyleft is both accepted and proposed by both parties: " Viral license " is a pejorative name for copyleft licenses. It originates from the terms 'General Public Virus' or 'GNU Public Virus' (GPV), which dates back to 1990, a year after the GPLv1

1080-419: A fee. Unlike similar permissive licenses that also grant these freedoms, copyleft licenses also ensure that any modified versions of a work covered by a copyleft license must also grant these freedoms. Thus, copyleft licenses have conditions: that modifications of any work licensed under a copyleft license must be distributed under a compatible copyleft scheme and that the distributed modified work must include

1200-621: A few others. The Fedora Project's distribution license guidelines were used as a basis for the FSDG. The Fedora Project's own guidelines, however, currently do not follow the FSDG, and thus the GNU Project does not consider Fedora to be a fully free (libre) GNU/Linux distribution. From the mid-1990s onward, with many companies investing in free software development, the Free Software Foundation redirected its funds toward

1320-484: A large legal settlement was paid. In the twenty-first century, Windows continues to be popular on personal computers but has less market share of servers. UNIX operating systems, especially Linux, are the most popular on enterprise systems and servers but are also used on mobile devices and many other computer systems. On mobile devices, Symbian OS was dominant at first, being usurped by BlackBerry OS (introduced 2002) and iOS for iPhones (from 2007). Later on,

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1440-589: A letter in 1984 or 1985, on which was written: "Copyleft – all rights reversed ", which is a pun on the common copyright disclaimer " all rights reserved ". In France , a series of meetings taking place in 2000 under the title "Copyleft Attitude" gave birth to the Free Art License (FAL), theoretically valid in any jurisdiction bound by the Berne Convention and recommended by Stallman's own Free Software Foundation . Shortly thereafter,

1560-442: A library with no protection between applications, such as eCos . A hypervisor is an operating system that runs a virtual machine . The virtual machine is unaware that it is an application and operates as if it had its own hardware. Virtual machines can be paused, saved, and resumed, making them useful for operating systems research, development, and debugging. They also enhance portability by enabling applications to be run on

1680-593: A license that allows one to use GNU GPL in combination with a limited warranty. For projects which will be run over a network, a variation of the GNU GPL, called the Affero General Public License (GNU AGPL), ensures that the source code is available to users of software over a network. Copyleft is a distinguishing feature of some free software licenses, while other free-software licenses are not copyleft licenses because they do not require

1800-447: A malformed machine instruction . However, the most common error conditions are division by zero and accessing an invalid memory address . Users can send messages to the kernel to modify the behavior of a currently running process. For example, in the command-line environment , pressing the interrupt character (usually Control-C ) might terminate the currently running process. To generate software interrupts for x86 CPUs,

1920-486: A means of modifying the work. Under fair use , however, copyleft licenses may be superseded, just like regular copyrights. Therefore, any person utilizing a source licensed under a copyleft license for works they invent is free to choose any other license (or none at all) provided they meet the fair use standard. Copyleft licenses necessarily make creative use of relevant rules and laws to enforce their provisions. For example, when using copyright law, those who contribute to

2040-455: A particular application's memory is stored, or even whether or not it has been allocated yet. In modern operating systems, memory which is accessed less frequently can be temporarily stored on a disk or other media to make that space available for use by other programs. This is called swapping , as an area of memory can be used by multiple programs, and what that memory area contains can be swapped or exchanged on demand. Virtual memory provides

2160-503: A program does not interfere with memory already in use by another program. Since programs time share, each program must have independent access to memory. Cooperative memory management, used by many early operating systems, assumes that all programs make voluntary use of the kernel 's memory manager, and do not exceed their allocated memory. This system of memory management is almost never seen any more, since programs often contain bugs which can cause them to exceed their allocated memory. If

2280-408: A program fails, it may cause memory used by one or more other programs to be affected or overwritten. Malicious programs or viruses may purposefully alter another program's memory, or may affect the operation of the operating system itself. With cooperative memory management, it takes only one misbehaved program to crash the system. Memory protection enables the kernel to limit a process' access to

2400-440: A program tries to access memory that is not accessible memory, but nonetheless has been allocated to it, the kernel is interrupted (see § Memory management ) . This kind of interrupt is typically a page fault . When the kernel detects a page fault it generally adjusts the virtual memory range of the program which triggered it, granting it access to the memory requested. This gives the kernel discretionary power over where

2520-420: A program's users, no matter what subsequent revisions anyone made to the original program. This original GPL did not grant rights to the public at large, only those who had already received the program; but it was the best that could be done under existing law. The new license was not at this time given the copyleft label. Richard Stallman stated that the use of "Copyleft" comes from Don Hopkins , who mailed him

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2640-644: A proprietary operating system. According to its manifesto, the founding goal of the project was to build a free operating system, and if possible, "everything useful that normally comes with a Unix system so that one could get along without any software that is not free." Development was initiated in January 1984. In 1991, the Linux kernel appeared, developed outside the GNU project by Linus Torvalds , and in December 1992 it

2760-406: A result, any user who obtains the software legally has the same freedoms as the rest of its users do. The GNU Project and the Free Software Foundation sometimes differentiate between "strong" and "weak" copyleft. "Weak" copyleft programs typically allow distributors to link them together with non-free programs, while "strong" copyleft strictly forbids this practice. Most of the GNU Project's output

2880-527: A separate, unrelated initiative in the United States yielded the Creative Commons license , available since 2001 in several different versions (only some of which can be described as copyleft) and more specifically tailored to U.S. law. While copyright law gives software authors control over copying, distribution and modification of their works, the goal of copyleft is to give all users of

3000-470: A significant amount of CPU time. Direct memory access (DMA) is an architecture feature to allow devices to bypass the CPU and access main memory directly. (Separate from the architecture, a device may perform direct memory access to and from main memory either directly or via a bus.) When a computer user types a key on the keyboard, typically the character appears immediately on the screen. Likewise, when

3120-402: A specific moment in time. Hard real-time systems require exact timing and are common in manufacturing , avionics , military, and other similar uses. With soft real-time systems, the occasional missed event is acceptable; this category often includes audio or multimedia systems, as well as smartphones. In order for hard real-time systems be sufficiently exact in their timing, often they are just

3240-417: A user moves a mouse , the cursor immediately moves across the screen. Each keystroke and mouse movement generates an interrupt called Interrupt-driven I/O . An interrupt-driven I/O occurs when a process causes an interrupt for every character or word transmitted. Devices such as hard disk drives , solid-state drives , and magnetic tape drives can transfer data at a rate high enough that interrupting

3360-453: A variation of the classic reader/writer problem . The writer receives a pipe from the shell for its output to be sent to the reader's input stream. The command-line syntax is alpha | bravo . alpha will write to the pipe when its computation is ready and then sleep in the wait queue. bravo will then be moved to the ready queue and soon will read from its input stream. The kernel will generate software interrupts to coordinate

3480-468: A version of GNU/Hurd that is suitable for production environments since the commencement of the GNU/Hurd project over 33 years ago. A stable version (or variant) of GNU can be run by combining the GNU packages with the Linux kernel , making a functional Unix-like system. The GNU project calls this GNU/Linux, and the defining features are the combination of: Within the GNU website, a list of projects

3600-417: A work (except the license itself) may only be modified and distributed under the terms of the work's copyleft license. Partial copyleft, by contrast, exempts some parts of the work from the copyleft provisions, permitting distribution of some modifications under terms other than the copyleft license, or in some other way does not impose all the principles of copylefting on the work. An example of partial copyleft

3720-410: A work the freedom and permission to reproduce, adapt , or distribute it, copyleft licenses are distinct from other types of copyright licenses that limit such freedoms. Instead of allowing a work to fall completely into the public domain , where no ownership of copyright is claimed, copyleft allows authors to impose restrictions on the use of their work. One of the main restrictions imposed by copyleft

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3840-490: A work under copyleft usually must gain, defer, or assign copyright holder status. By submitting the copyright of their contributions under a copyleft license, they deliberately give up some of the rights that normally follow from copyright, including the right to be the unique distributor of copies of the work. Some laws used for copyleft licenses vary from one country to another, and may also be granted in terms that vary from country to country. For example, in some countries, it

3960-562: Is remote direct memory access , which enables each CPU to access memory belonging to other CPUs. Multicomputer operating systems often support remote procedure calls where a CPU can call a procedure on another CPU, or distributed shared memory , in which the operating system uses virtualization to generate shared memory that does not physically exist. A distributed system is a group of distinct, networked computers—each of which might have their own operating system and file system. Unlike multicomputers, they may be dispersed anywhere in

4080-428: 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 also include accounting software for cost allocation of processor time , mass storage , peripherals, and other resources. For hardware functions such as input and output and memory allocation ,

4200-484: Is a change away from the currently running process. Similarly, both hardware and software interrupts execute an interrupt service routine . Software interrupts may be normally occurring events. It is expected that a time slice will occur, so the kernel will have to perform a context switch . A computer program may set a timer to go off after a few seconds in case too much data causes an algorithm to take too long. Software interrupts may be error conditions, such as

4320-757: Is a mirrored version of the copyright symbol , © : a reversed C in a circle. A 2016 proposal to add the symbol to a future version of Unicode was accepted by the Unicode Technical Committee . The code point U+1F12F 🄯 COPYLEFT SYMBOL was added in Unicode 11 . The copyleft symbol has no legal status. As of 2024, the symbol is generally provided as standard in the system fonts of most current operating systems , but if need be it may be approximated with character U+2184 ↄ LATIN SMALL LETTER REVERSED C between parenthesis (ɔ) . On modern computer systems,

4440-555: Is acceptable to sell a software product without warranty, in standard GNU General Public License style, while in most European countries it is not permitted for a software distributor to waive all warranties regarding a sold product. For this reason, the extent of such warranties is specified in most European copyleft licenses, for example, the European Union Public Licence (EUPL), or the CeCILL license ,

4560-711: Is copyleft under the Creative Commons Attribution-ShareAlike license. Li-Chen Wang 's Palo Alto Tiny BASIC for the Intel 8080 appeared in Dr. Dobb's Journal in May 1976. The listing begins with the title, author's name, and date, but also has "@COPYLEFT ALL WRONGS RESERVED". The concept of copyleft was described in Richard Stallman 's GNU Manifesto in 1985, where he wrote: GNU

4680-623: Is designed to collect Enterprise software for the GNU system in a single location (much like the GNOME project collects Desktop software),it was later Decommissioned . In 2001, the GNU Project received the USENIX Lifetime Achievement Award for "the ubiquity, breadth, and quality of its freely available redistributable and modifiable software, which has enabled a generation of research and commercial development". Operating system An operating system ( OS )

4800-401: Is determined by the extent to which its provisions can be imposed on all kinds of derivative works. Thus, the term "weak copyleft" refers to licenses where not all derivative works inherit the copyleft license; whether a derivative work inherits or not often depends on how it was derived. "Weak copyleft" licenses are often used to cover software libraries . This allows other software to link to

4920-422: Is difficult to define, but has been called "the layer of software that manages a computer's resources for its users and their applications ". Operating systems include the software that is always running, called a kernel —but can include other software as well. The two other types of programs that can run on a computer are system programs —which are associated with the operating system, but may not be part of

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5040-487: Is laid out and each project has specifics for what type of developer is able to perform the task needed for a certain piece of the GNU project. The skill level ranges from project to project but anyone with background knowledge in programming is encouraged to support the project. The packaging of GNU tools, together with the Linux kernel and other programs, is usually called a Linux distribution (distro). The GNU Project calls

5160-427: Is more important than a copyleft. Common practice for using copyleft is to codify the copying terms for a work with a license . Any such license typically includes all the provisions and principles of copyleft inside the license's terms. This includes the freedom to use the work, study the work, copy, and share the work with others, modify the work, and distribute exact or modified versions of that work, with or without

5280-479: Is no reason to believe the GPL could force proprietary software to become free software, but could "try to enjoin the firm from distributing commercially a program that combined with the GPL'd code to form a derivative work, and to recover damages for infringement." If the firm "actually copied code from a GPL'd program, such a suit would be a perfectly ordinary assertion of copyright, which most private firms would defend if

5400-400: Is not in the public domain. Everyone will be permitted to modify and redistribute GNU, but no distributor will be allowed to restrict its further redistribution. That is to say, proprietary modifications will not be allowed. I want to make sure that all versions of GNU remain free. Stallman's motivation was that a few years earlier he had worked on a Lisp interpreter. Symbolics asked to use

5520-443: Is only a single application running, at least conceptually, so there is no need to prevent interference between applications) and OS services are accessed via simple library calls (potentially inlining them based on compiler thresholds), without the usual overhead of context switches , in a way similarly to embedded and real-time OSes. Note that this overhead is not negligible: to the direct cost of mode switching it's necessary to add

5640-486: Is released under a strong copyleft, although some is released under a weak copyleft or a lax, push-over free software license. The first goal of the GNU project was to create a whole free-software operating system. Because UNIX was already widespread and ran on more powerful machines, compared to contemporary CP/M or MS-DOS machines of time, it was decided it would be a Unix-like operating system. Richard Stallman later commented that he considered MS-DOS "a toy". By 1992,

5760-499: Is supported by most UNIX systems. MINIX was a stripped-down version of UNIX, developed in 1987 for educational uses, that inspired the commercially available, free software Linux . Since 2008, MINIX is used in controllers of most Intel microchips , while Linux is widespread in data centers and Android smartphones. The invention of large scale integration enabled the production of personal computers (initially called microcomputers ) from around 1980. For around five years,

5880-421: Is that derived works must also be released under a compatible copyleft license. This is due to the underlying principle of copyleft: that anyone can benefit freely from the previous work of others, but that any modifications to that work should benefit everyone else as well, and thus must be released under similar terms. For this reason, copyleft licenses are also known as reciprocal licenses: any modifiers of

6000-525: Is that not everyone wants to share their work, and some share-alike agreements require that the whole body of work be shared, even if the author only wants to share a certain part. The plus side for an author of source code is that any modification to the code will not only benefit the original author but that the author will be recognized and ensure the same or compatible license terms cover the changed code. Some Creative Commons licenses are examples of share-alike copyleft licenses. Those licenses grant users of

6120-473: Is that they do not load user-installed software. Consequently, they do not need protection between different applications, enabling simpler designs. Very small operating systems might run in less than 10 kilobytes , and the smallest are for smart cards . Examples include Embedded Linux , QNX , VxWorks , and the extra-small systems RIOT and TinyOS . A real-time operating system is an operating system that guarantees to process events or data by or at

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6240-496: Is the GPL linking exception made for some software packages. The " share-alike " condition in some licenses imposes the requirement that any freedom that is granted regarding the original work must be granted on exactly the same or compatible terms in any derived work. This implies that any copyleft license is automatically a share-alike license but not the other way around, as some share-alike licenses include further restrictions such as prohibiting commercial use. Another restriction

6360-435: Is the part of the operating system that provides protection between different applications and users. This protection is key to improving reliability by keeping errors isolated to one program, as well as security by limiting the power of malicious software and protecting private data, and ensuring that one program cannot monopolize the computer's resources. Most operating systems have two modes of operation: in user mode ,

6480-560: Is the same detailed history as at their web site. The GNU Manifesto was written by Richard Stallman to gain support and participation in the GNU Project. In the GNU Manifesto, Stallman listed four freedoms essential to software users: freedom to run a program for any purpose, freedom to study the mechanics of the program and modify it, freedom to redistribute copies, and freedom to improve and change modified versions for public use. To implement these freedoms, users needed full access to

6600-542: The CP/M (Control Program for Microcomputers) was the most popular operating system for microcomputers. Later, IBM bought the DOS (Disk Operating System) from Microsoft . After modifications requested by IBM, the resulting system was called MS-DOS (MicroSoft Disk Operating System) and was widely used on IBM microcomputers. Later versions increased their sophistication, in part by borrowing features from UNIX. Apple 's Macintosh

6720-558: The GNU General Public License (GPL), originally written by Richard Stallman , which was the first software copyleft license to see extensive use; the Mozilla Public License ; the Free Art License ; and the Creative Commons share-alike license condition —with the last two being intended for non-software works, such as documents and pictures, both academic or artistic in nature. Misplaced Pages

6840-552: The GNU Lesser General Public License and the Mozilla Public License . The GNU General Public License is an example of a license implementing strong copyleft. An even stronger copyleft license is the AGPL , which requires the publishing of the source code for software as a service use cases. The Sybase Open Watcom Public License is one of the strongest copyleft licenses, as this license closes

6960-504: The INT assembly language instruction is available. The syntax is INT X , where X is the offset number (in hexadecimal format) to the interrupt vector table . To generate software interrupts in Unix-like operating systems, the kill(pid,signum) system call will send a signal to another process. pid is the process identifier of the receiving process. signum is

7080-458: The kernel and the compiler were finished, GNU was able to be used for program development . The main goal was to create many other applications to be like the Unix system. GNU was able to run Unix programs but was not identical to it. GNU incorporated longer file names, file version numbers, and a crash-proof file system. The GNU Manifesto was written to gain support and participation from others for

7200-498: The personal computer market, as of September 2024 , Microsoft Windows holds a dominant market share of around 73%. macOS by Apple Inc. is in second place (15%), Linux is in third place (5%), and ChromeOS is in fourth place (2%). In the mobile sector (including smartphones and tablets ), as of September 2023 , Android's share is 68.92%, followed by Apple's iOS and iPadOS with 30.42%, and other operating systems with .66%. Linux distributions are dominant in

7320-415: The source code . To ensure code remained free and provide it to the public, Stallman created the GNU General Public License (GPL), which allowed software and the future generations of code derived from it to remain free for public use. Although most of the GNU Project's output is technical in nature, it was launched as a social, ethical, and political initiative. As well as producing software and licenses,

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7440-420: The transistor in the mid-1950s, mainframes began to be built. These still needed professional operators who manually do what a modern operating system would do, such as scheduling programs to run, but mainframes still had rudimentary operating systems such as Fortran Monitor System (FMS) and IBSYS . In the 1960s, IBM introduced the first series of intercompatible computers ( System/360 ). All of them ran

7560-410: The CPU for every byte or word transferred, and having the CPU transfer the byte or word between the device and memory, would require too much CPU time. Data is, instead, transferred between the device and memory independently of the CPU by hardware such as a channel or a direct memory access controller; an interrupt is delivered only when all the data is transferred. If a computer program executes

7680-474: The CPU to re-enter supervisor mode , placing the kernel in charge. This is called a segmentation violation or Seg-V for short, and since it is both difficult to assign a meaningful result to such an operation, and because it is usually a sign of a misbehaving program, the kernel generally resorts to terminating the offending program, and reports the error. Windows versions 3.1 through ME had some level of memory protection, but programs could easily circumvent

7800-668: The FSF asserts it does not and explicitly adds an exception allowing it in the license for the GNU Classpath re-implementation of the Java library. This ambiguity is an important difference between the GPL and the LGPL , in that the LGPL specifically allows linking or compiling works licensed under terms that are not compatible with the LGPL, with works covered by the LGPL. The copyleft symbol

7920-423: The GNU Project has published a number of writings, the majority of which were authored by Richard Stallman. The GNU project uses software that is free for users to copy, edit, and distribute. It is free in the sense that users can change the software to fit individual needs. The way programmers obtain the free software depends on where they get it. The software could be provided to the programmer from friends or over

8040-473: The GNU Project in a Usenet message in September 1983. Despite never having used Unix prior, Stallman felt that it was the most appropriate system design to use as a basis for the GNU Project, as it was portable and "fairly clean". When the GNU project first started they had an Emacs text editor with Lisp for writing editor commands, a source level debugger , a yacc -compatible parser generator, and

8160-534: The GNU Project is owned by the Free Software Foundation. The GNOME desktop effort was launched by the GNU Project because another desktop system, KDE , was becoming popular but required users to install Qt , which was then proprietary software . To prevent people from being tempted to install KDE and Qt, the GNU Project simultaneously launched two projects. One was the Harmony toolkit . This

8280-456: The GNU project had completed all of the major operating system utilities, but had not completed their proposed operating system kernel , GNU Hurd . With the release of the Linux kernel , started independently by Linus Torvalds in 1991, and released under the GPLv2 with version 0.12 in 1992, for the first time it was possible to run an operating system composed completely of free software. Though

8400-464: The GPL poses a threat to the intellectual property of any organization making use of it." In another context, Steve Ballmer declared that code released under GPL is useless to the commercial sector, since it can only be used if the resulting surrounding code is licensed under a GPL-compatible license, and described it thus as "a cancer that attaches itself in an intellectual property sense to everything it touches". In response to Microsoft's attacks on

8520-433: The GPL, several prominent free-software developers and advocates released a joint statement supporting the license. According to FSF compliance engineer David Turner, the term "viral license" creates a misunderstanding and a fear of using copylefted free software. While a person can catch a virus without active action, license conditions take effect upon effective usage or adoption. David McGowan has also written that there

8640-459: The Internet, or the company a programmer works for may purchase the software. Proceeds from associate members, purchases, and donations support the GNU Project. Copyleft is what helps maintain free use of this software among other programmers. Copyleft gives the legal right to everyone to use, edit, and redistribute programs or programs' code as long as the distribution terms do not change. As

8760-505: The Linux kernel is not part of the GNU project, it was developed using GCC and other GNU programming tools and was released as free software under the GNU General Public License . Most compilation of the Linux kernel is still done with GNU toolchains, but it is currently possible to use the Clang compiler and the LLVM toolchain for compilation. As of present, the GNU project has not released

8880-485: The Lisp interpreter, and Stallman agreed to supply them with a public domain version of his work. Symbolics extended and improved the Lisp interpreter, but when Stallman wanted access to the improvements that Symbolics had made to his interpreter, Symbolics refused. Stallman then, in 1984, proceeded to work towards eradicating this emerging behavior and culture of proprietary software , which he named software hoarding . This

9000-538: The application program, which then interacts with the user and with hardware devices. However, in some systems an application can request that the operating system execute another application within the same process, either as a subroutine or in a separate thread, e.g., the LINK and ATTACH facilities of OS/360 and successors . An interrupt (also known as an abort , exception , fault , signal , or trap ) provides an efficient way for most operating systems to react to

9120-493: The availability of both types of licenses, copyleft and permissive, allow authors to choose the type under which to license the works they invent. For documents, art, and other works other than software and code, the Creative Commons share-alike licensing system and the GNU Free Documentation License (GFDL) allow authors to apply limitations to certain sections of their work, exempting some parts of

9240-622: The combination of GNU and the Linux kernel "GNU/Linux", and asks others to do the same, resulting in the GNU/Linux naming controversy . Most Linux distros combine GNU packages with a Linux kernel which contains proprietary binary blobs . The GNU Free System Distribution Guidelines (GNU FSDG) is a system distribution commitment that explains how an installable system distribution (such as a Linux distribution) qualifies as free (libre), and helps distribution developers make their distributions qualify. The list mostly describes distributions that are

9360-456: The communication is abstract, such as executing a command-line tool with a set of switches or interacting with a web server. As a consequence, even if one module of an otherwise non-copyleft product is placed under the GPL, it may still be legal for other components to communicate with it in ways such as these. This allowed communication may or may not include reusing libraries or routines via dynamic linking  – some commentators say it does,

9480-453: The computer's memory. Various methods of memory protection exist, including memory segmentation and paging . All methods require some level of hardware support (such as the 80286 MMU), which does not exist in all computers. In both segmentation and paging, certain protected mode registers specify to the CPU what memory address it should allow a running program to access. Attempts to access other addresses trigger an interrupt, which causes

9600-471: The details of how interrupt service routines behave vary from operating system to operating system. However, several interrupt functions are common. The architecture and operating system must: A software interrupt is a message to a process that an event has occurred. This contrasts with a hardware interrupt — which is a message to the central processing unit (CPU) that an event has occurred. Software interrupts are similar to hardware interrupts — there

9720-422: The environment. Interrupts cause the central processing unit (CPU) to have a control flow change away from the currently running program to an interrupt handler , also known as an interrupt service routine (ISR). An interrupt service routine may cause the central processing unit (CPU) to have a context switch . The details of how a computer processes an interrupt vary from architecture to architecture, and

9840-410: The hardware checks that the software is only executing legal instructions, whereas the kernel has unrestricted powers and is not subject to these checks. The kernel also manages memory for other processes and controls access to input/output devices. The operating system provides an interface between an application program and the computer hardware, so that an application program can interact with

9960-493: The hardware only by obeying rules and procedures programmed into the operating system. The operating system is also a set of services which simplify development and execution of application programs. Executing an application program typically involves the creation of a process by the operating system kernel , which assigns memory space and other resources, establishes a priority for the process in multi-tasking systems, loads program binary code into memory, and initiates execution of

10080-418: The indirect pollution of important processor structures (like CPU caches , the instruction pipeline , and so on) which affects both user-mode and kernel-mode performance. The first computers in the late 1940s and 1950s were directly programmed either with plugboards or with machine code inputted on media such as punch cards , without programming languages or operating systems. After the introduction of

10200-404: The interrupt request, the operating system will: When the writing process has its time slice expired, the operating system will: With the program counter now reset, the interrupted process will resume its time slice. Among other things, a multiprogramming operating system kernel must be responsible for managing all system memory which is currently in use by the programs. This ensures that

10320-431: The kernel—and applications—all other software. There are three main purposes that an operating system fulfills: With multiprocessors multiple CPUs share memory. A multicomputer or cluster computer has multiple CPUs, each of which has its own memory . Multicomputers were developed because large multiprocessors are difficult to engineer and prohibitively expensive; they are universal in cloud computing because of

10440-529: The legal and political support of free software development. Software development from that point on focused on maintaining existing projects, and starting new projects only when there was an acute threat to the free software community . One of the most notable projects of the GNU Project is the GNU Compiler Collection , whose components have been adopted as the standard compiler system on many Unix-like systems. The copyright of most works by

10560-558: The library and be redistributed without the requirement for the linking software to also be licensed under the same terms. Only changes to the software licensed under a "weak copyleft" license become subject itself to copyleft provisions of such a license. This allows programs of any license to be compiled and linked against copylefted libraries such as glibc and then redistributed without any re-licensing required. The concrete effect of strong vs. weak copyleft has yet to be tested in court. Free-software licenses that use "weak" copyleft include

10680-438: The licensee to distribute derivative works under the same license. There is an ongoing debate as to which class of license provides the greater degree of freedom. This debate hinges on complex issues, such as the definition of freedom and whose freedoms are more important: the potential future recipients of a work (freedom from proprietization) or just the initial recipient (freedom to proprietize). However, current copyright law and

10800-400: The memory allocated to a different one. Around the same time, teleprinters began to be used as terminals so multiple users could access the computer simultaneously. The operating system MULTICS was intended to allow hundreds of users to access a large computer. Despite its limited adoption, it can be considered the precursor to cloud computing . The UNIX operating system originated as

10920-408: The need to use it. A general protection fault would be produced, indicating a segmentation violation had occurred; however, the system would often crash anyway. The use of virtual memory addressing (such as paging or segmentation) means that the kernel can choose what memory each program may use at any given time, allowing the operating system to use the same memory locations for multiple tasks. If

11040-408: The open-source Android operating system (introduced 2008), with a Linux kernel and a C library ( Bionic ) partially based on BSD code, became most popular. The components of an operating system are designed to ensure that various parts of a computer function cohesively. With the de facto obsoletion of DOS , all user software must interact with the operating system to access hardware. The kernel

11160-420: The operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently 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 . In

11280-421: The piping. Signals may be classified into 7 categories. The categories are: Input/output (I/O) devices are slower than the CPU. Therefore, it would slow down the computer if the CPU had to wait for each I/O to finish. Instead, a computer may implement interrupts for I/O completion, avoiding the need for polling or busy waiting. Some computers require an interrupt for each character or word, costing

11400-407: The programmer or the user with the perception that there is a much larger amount of RAM in the computer than is really there. Copyleft Higher categories: Software , freedom Copyleft is the legal technique of granting certain freedoms over copies of copyrighted works with the requirement that the same rights be preserved in derivative works . In this sense, freedoms refers to

11520-490: The project. Programmers were encouraged to take part in any aspect of the project that interested them. People could donate funds, computer parts, or even their own time to write code and programs for the project. The origins and development of most aspects of the GNU Project (and free software in general) are shared in a detailed narrative in the Emacs help system. (C-h g runs the Emacs editor command describe-gnu-project .) It

11640-534: The proprietary component that KDE depended on ( Qt ) was released as free software. GNOME has since dissociated itself from the GNU Project and the Free Software Foundation, and is now independently managed by the GNOME Project . GNU Enterprise ( GNUe ) was a meta-project started in 1996, and can be regarded as a sub-project of the GNU Project. GNUe's goal is to create free "enterprise-class data-aware applications" ( enterprise resource planners , etc.). GNUe

11760-427: The quality of their software to compete with free software. This may also have the effect of preventing monopolies in areas dominated by proprietary software. However, competition with proprietary software can also be a reason to forgo copyleft. The Free Software Foundation recommends that when "widespread use of the code is vital for advancing the cause of free software", allowing the code to be copied and used freely

11880-418: The same operating system— OS/360 —which consisted of millions of lines of assembly language that had thousands of bugs . The OS/360 also was the first popular operating system to support multiprogramming , such that the CPU could be put to use on one job while another was waiting on input/output (I/O). Holding multiple jobs in memory necessitated memory partitioning and safeguards against one job accessing

12000-619: The server and supercomputing sectors. Other specialized classes of operating systems (special-purpose operating systems), such as embedded and real-time systems, exist for many applications. Security-focused operating systems also exist. Some operating systems have low system requirements (e.g. light-weight Linux distribution ). Others may have higher system requirements. Some operating systems require installation or may come pre-installed with purchased computers ( OEM -installation), whereas others may run directly from media (i.e. live CD ) or flash memory (i.e. USB stick). An operating system

12120-411: The shoe were on the other foot." Richard Stallman has described this view with an analogy, saying, "The GPL's domain does not spread by proximity or contact, only by deliberate inclusion of GPL-covered code in your program. It spreads like a spider plant , not like a virus." Popular copyleft licenses, such as the GPL, have a clause allowing components to interact with non-copyleft components as long as

12240-400: The signal number (in mnemonic format) to be sent. (The abrasive name of kill was chosen because early implementations only terminated the process.) In Unix-like operating systems, signals inform processes of the occurrence of asynchronous events. To communicate asynchronously, interrupts are required. One reason a process needs to asynchronously communicate to another process solves

12360-400: The size of the machine needed. The different CPUs often need to send and receive messages to each other; to ensure good performance, the operating systems for these machines need to minimize this copying of packets . Newer systems are often multiqueue —separating groups of users into separate queues —to reduce the need for packet copying and support more concurrent users. Another technique

12480-661: The so-called "private usage" loophole of the GPL, and requires the publishing of source code in any use case. For this reason, the license is considered non-free by the Free Software Foundation , the GNU Project , and the Debian project. However, the license is accepted as open source by the OSI . The Design Science License (DSL) is a strong copyleft license that applies to any work, not only software or documentation, but also literature, artworks, music, photography, and video. DSL

12600-490: The software the same freedoms as copyleft licenses but do not require modified versions of that software to also include those freedoms. They have minimal restrictions on how the software can be used, modified, and redistributed, and are thus not copyleft licenses. Examples of this type of license include the X11 license , Apache license , Expat license , and the various BSD licenses . It has been suggested that copyleft has become

12720-698: The software. Some creators, such as Elastic , feel that preventing commercial enterprises from using and then selling their product under a proprietary license is also an incentive. Furthermore, the open-source culture of programming has been described as a gift economy , where social power is determined by an individual's contributions. Contributing to or creating open-source, copyleft-licensed software of high quality can lead to contributors gaining valuable experience and can lead to future career opportunities. Copyleft software has economic effects beyond individual creators. The presence of quality copyleft software can force proprietary software developers to increase

12840-570: The use of the work for any purpose, and the ability to modify, copy, share, and redistribute the work, with or without a fee. Licenses which implement copyleft can be used to maintain copyright conditions for works ranging from computer software , to documents , art , and scientific discoveries, and similar approaches have even been applied to certain patents . Copyleft software licenses are considered protective or reciprocal in contrast with permissive free software licenses , and require that information necessary for reproducing and modifying

12960-525: The work and its derivatives to be provided in a form that allows further modifications to be made. In software , this means requiring that the source code of the derived work be made available together with the software itself. The economic incentives to work on copyleft content can vary. Traditional copyright law is designed to promote progress by providing economic benefits to creators. When choosing to copyleft their work, content creators may seek complementary benefits like recognition from their peers. In

13080-453: The work from the full copyleft mechanism. In the case of the GFDL, these limitations include the use of invariant sections, which may not be altered by future editors. The initial intention of the GFDL was as a device for supporting the documentation of copylefted software. However, the result is that it can be used for any kind of document. The strength of the copyleft license governing a work

13200-464: The work must be made available to recipients of the software program, which are often distributed as executables . This information is most commonly in the form of source code files, which usually contain a copy of the license terms and acknowledge the authors of the code. Copyleft helps ensure everyone's rights to freely use the product but it prohibits owning, registering copyright and earning royalties from copyright. Notable copyleft licenses include

13320-632: The work the freedom to carry out all of these activities. These freedoms (from the Free Software Definition ) include: Similar terms are present in the Open Source Definition , a separate definition that contains similar freedoms. The vast majority of copyleft licenses satisfy both definitions, that of the Free Software Definition and Open Source Definition. By guaranteeing viewers and users of

13440-494: The world of computer programming, copyleft-licensed computer programs are often created by programmers to fill a need they have noticed. Such programs are often published with a copyleft license simply to ensure that subsequent users can also freely use modified versions of that program. This is especially true for creators who wish to prevent "open source hijacking", or the act of reusing open-source code and then adding extra restrictions to it, an action prevented by copyleft-licensing

13560-473: The world. Middleware , an additional software layer between the operating system and applications, is often used to improve consistency. Although it functions similarly to an operating system, it is not a true operating system. Embedded operating systems are designed to be used in embedded computer systems , whether they are internet of things objects or not connected to a network. Embedded systems include many household appliances. The distinguishing factor

13680-540: The wrongs he perceived it to perpetuate, he decided to work within the framework of existing law; in 1985, he created his own copyright license, the Emacs General Public License, the first copyleft license. This later evolved into the GNU General Public License , which is now one of the most popular free-software licenses. For the first time, a copyright holder had taken steps to ensure that the maximal number of rights be perpetually transferred to

13800-463: Was an attempt to make a free software replacement for Qt. Had this project been successful, the perceived problem with the KDE would have been solved. The second project was GNOME, which tackled the same issue from a different angle. It aimed to make a replacement for KDE that had no dependencies on proprietary software. The Harmony project did not make much progress, but GNOME developed very well. Eventually,

13920-435: Was made available under version 2 of the GNU General Public License . Combined with the operating system utilities already developed by the GNU project, it allowed for the first operating system that was free software, commonly known as Linux . The project's current work includes software development, awareness building, political campaigning, and sharing of new material. Richard Stallman announced his intent to start coding

14040-436: Was not the first time Stallman had dealt with proprietary software, but he deemed this interaction a "turning point". He justified software sharing, protesting that when sharing, the software online can be copied without the loss of the original piece of work. The software can be used multiple times without ever being damaged or worn out. As Stallman deemed it impractical in the short term to eliminate current copyright law and

14160-502: Was released. The name 'viral license' refers to the fact that any works derived from a copyleft work must preserve the copyleft permissions when distributed. Some advocates of the various BSD Licenses used the term derisively in regards to the GPL's tendency to absorb BSD-licensed code without allowing the original BSD work to benefit from it, while at the same time promoting itself as "freer" than other licenses. Microsoft vice-president Craig Mundie remarked, "This viral aspect of

14280-406: Was the first popular computer to use a graphical user interface (GUI). The GUI proved much more user friendly than the text-only command-line interface earlier operating systems had used. Following the success of Macintosh, MS-DOS was updated with a GUI overlay called Windows . Windows later was rewritten as a stand-alone operating system, borrowing so many features from another ( VAX VMS ) that

14400-408: Was written by Michael Stutz after he took an interest in applying GNU-style copyleft to non-software works, which later came to be called libre works . In the 1990s, it was used on music recordings, visual art, and even novels. It is not considered compatible with the GNU GPL by the Free Software Foundation. "Full" and "partial" copyleft relate to another issue. Full copyleft exists when all parts of

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