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82-541: Early research and development: Merging the networks and creating the Internet: Commercialization, privatization, broader access leads to the modern Internet: Examples of Internet services: Unix ( / ˈ j uː n ɪ k s / , YOO -niks ; trademarked as UNIX ) is a family of multitasking , multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at

164-435: A swap file or swap partition is a way for the operating system to provide more memory than is physically available by keeping portions of the primary memory in secondary storage . While multitasking and memory swapping are two completely unrelated techniques, they are very often used together, as swapping memory allows more tasks to be loaded at the same time. Typically, a multitasking system allows another process to run when

246-429: A time-sharing configuration, as well as portability. 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

328-482: 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

410-518: A 1999 interview, Dennis Ritchie voiced his opinion that Linux and BSD Unix 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 among the healthiest of the direct Unix derivatives, though there are also the various BSD systems as well as

492-466: A Program Distributor feeding up to twenty-five autonomous processing units with code and data, and allowing concurrent operation of multiple clusters. Another such computer was the LEO III , first released in 1961. During batch processing , several different programs were loaded in the computer memory, and the first one began to run. When the first program reached an instruction waiting for a peripheral,

574-468: A computer's memory, allowing the CPU to switch between them swiftly. This optimizes CPU utilization by keeping it engaged with the execution of tasks, particularly useful when one program is waiting for I/O operations to complete. The Bull Gamma 60 , initially designed in 1957 and first released in 1960, was the first computer designed with multiprogramming in mind. Its architecture featured a central memory and

656-454: 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, and as users added their own tools to the system and shared them with colleagues. At first, Unix was not designed to support multi-tasking or to be portable . Later, Unix gradually gained multi-tasking and multi-user capabilities in

738-664: A debugger, manual timing (of overall program or section of code) instead of a profiler, or tracking bugs in a text file or spreadsheet instead of a bug tracking system. The distinction between tools and applications is murky. For example, developers use simple databases (such as a file containing a list of important values ) all the time as tools. However a full-blown database is usually thought of as an application or software in its own right. For many years, computer-assisted software engineering (CASE) tools were sought. Successful tools have proven elusive. In one sense, CASE tools emphasized design and architecture support, such as for UML. But

820-415: A generic term such as system to help avoid the creation of a genericized trademark . Computer multitasking Multitasking does not require parallel execution of multiple tasks at exactly the same time; instead, it allows more than one task to advance over a given period of time. Even on multiprocessor computers, multitasking allows many more tasks to be run than there are CPUs. Multitasking

902-425: A human write-able and readable source language into the bits and bytes that can be executed by a computer. Interpreters interpret the program on the fly to produce the desired behavior. These programs perform many well defined and repetitive tasks that would nonetheless be time-consuming and error-prone when performed by a human, like laying out parts of a program in memory and fixing up the references between parts of

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984-404: 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 as a pun on Multics , which stood for Multiplexed Information and Computer Services . Brian Kernighan takes credit for

1066-510: 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

1148-405: A program as a linker does. Optimizing compilers on the other hand can perform complex transformations on the source code in order to improve the execution speed or other characteristics of a program. This allows a programmer to focus more on higher level, conceptual aspects of a program without worrying about the details of the machine it is running on. Because of the high complexity of software, it

1230-523: A program will run in a timely manner. Indeed, the first program may very well run for hours without needing access to a peripheral. As there were no users waiting at an interactive terminal, this was no problem: users handed in a deck of punched cards to an operator, and came back a few hours later for printed results. Multiprogramming greatly reduced wait times when multiple batches were being processed. Early multitasking systems used applications that voluntarily ceded time to one another. This approach, which

1312-420: A reference directory layout for Unix-like operating systems; it has mainly been used in Linux. 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

1394-504: 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 always be used as an adjective followed by

1476-449: 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 formed

1558-486: 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". By the early 1980s, users began seeing Unix as

1640-543: A single nine-track magnetic tape , earning its reputation as a portable system. 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 has the canonical early structure: The Unix system had a significant impact on other operating systems. It achieved its reputation by its interactivity, by providing

1722-466: A single processor might be shared between calculations of machine movement, communications, and user interface. Often multitasking operating systems include measures to change the priority of individual tasks, so that important jobs receive more processor time than those considered less significant. Depending on the operating system, a task might be as large as an entire application program, or might be made up of smaller threads that carry out portions of

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1804-557: A software developer uses some programming tools to visualize all kinds of information about programs. For example, a debugger allows a programmer to extract information about a running program in terms of the source language used to program it. The debugger can compute the value of a variable in the source program from the state of the concrete machine by using information stored by the compiler. Memory debuggers can directly point out questionable or outright wrong memory accesses of running programs which may otherwise remain undetected and are

1886-479: 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

1968-500: A variant to threads, named fibers , that are scheduled cooperatively. On operating systems that do not provide fibers, an application may implement its own fibers using repeated calls to worker functions. Fibers are even more lightweight than threads, and somewhat easier to program with, although they tend to lose some or all of the benefits of threads on machines with multiple processors . Some systems directly support multithreading in hardware . Essential to any multitasking system

2050-508: A versatile document preparation system, and an efficient file system featuring sophisticated access control, mountable and de-mountable volumes, and a unified treatment of peripherals as special files ." The latter permitted the Network Control Program (NCP) to be integrated within the Unix file system, treating network connections as special files that could be accessed through standard Unix I/O calls , which included

2132-402: A wider variety of machine families than any other operating system. The Unix 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

2214-473: Is a computer program that software developers use to create, debug, maintain, or otherwise support other programs and applications. The term usually refers to relatively simple programs, that can be combined to accomplish a task, much as one might use multiple hands to fix a physical object. The most basic tools are a source code editor and a compiler or interpreter , which are used ubiquitously and continuously. Other tools are used more or less depending on

2296-410: Is a common feature of computer operating systems since at least the 1960s. It allows more efficient use of the computer hardware; when a program is waiting for some external event such as a user input or an input/output transfer with a peripheral to complete, the central processor can still be used with another program. In a time-sharing system, multiple human operators use the same processor as if it

2378-402: Is not possible to understand most programs at a single glance even for the most experienced software developer. The abstractions provided by high-level programming languages also make it harder to understand the connection between the source code written by a programmer and the actual program's behaviour. In order to find bugs in programs and to prevent creating new bugs when extending a program,

2460-400: Is still used today on RISC OS systems. As a cooperatively multitasked system relies on each process regularly giving up time to other processes on the system, one poorly designed program can consume all of the CPU time for itself, either by performing extensive calculations or by busy waiting ; both would cause the whole system to hang . In a server environment, this is a hazard that makes

2542-400: Is to safely and effectively share access to system resources. Access to memory must be strictly managed to ensure that no process can inadvertently or deliberately read or write to memory locations outside the process's address space. This is done for the purpose of general system stability and data integrity, as well as data security. In general, memory access management is a responsibility of

Unix - Misplaced Pages Continue

2624-608: 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 ), Sun Microsystems ( SunOS / Solaris ), HP / HPE ( HP-UX ), and IBM ( AIX ). Early versions of Unix ran on PDP-11 computers; Unix

2706-682: The Classic Mac OS . In 2001 Apple switched to the NeXTSTEP -influenced Mac OS X . A similar model is used in Windows 9x and the Windows NT family , where native 32-bit applications are multitasked preemptively. 64-bit editions of Windows, both for the x86-64 and Itanium architectures, no longer support legacy 16-bit applications, and thus provide preemptive multitasking for all supported applications. Another reason for multitasking

2788-781: 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 , Ubuntu , Linux Mint , Slackware Linux , Arch Linux and Gentoo . A free derivative of BSD Unix, 386BSD ,

2870-480: The Sinclair QL followed in 1984, but it was not a big success. Commodore's Amiga was released the following year, offering a combination of multitasking and multimedia capabilities. Microsoft made preemptive multitasking a core feature of their flagship operating system in the early 1990s when developing Windows NT 3.1 and then Windows 95 . In 1988 Apple offered A/UX as a UNIX System V -based alternative to

2952-574: 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 that have been licensed to use the UNIX trademark include AIX , EulerOS , HP-UX , Inspur K-UX , IRIX , macOS , Solaris , Tru64 UNIX (formerly "Digital UNIX", or OSF/1 ), and z/OS . Notably, EulerOS and Inspur K-UX are Linux distributions certified as UNIX 03 compliant. Sometimes

3034-429: The CPU (" CPU bound "). In primitive systems, the software would often " poll ", or " busywait " while waiting for requested input (such as disk, keyboard or network input). During this time, the system was not performing useful work. With the advent of interrupts and preemptive multitasking, I/O bound processes could be "blocked", or put on hold, pending the arrival of the necessary data, allowing other processes to utilize

3116-569: The CPU. As the arrival of the requested data would generate an interrupt, blocked processes could be guaranteed a timely return to execution. Possibly the earliest preemptive multitasking OS available to home users was Microware 's OS-9 , available for computers based on the Motorola 6809 such as the TRS-80 Color Computer 2 , with the operating system supplied by Tandy as an upgrade for disk-equipped systems. Sinclair QDOS on

3198-487: 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 different Unix systems operating on the same CPU architecture. The Filesystem Hierarchy Standard was created to provide

3280-491: The UNIX trademark to The Open Group , an industry consortium founded in 1996. The Open Group allows the use of the mark for certified operating systems that comply with the Single UNIX Specification (SUS). Unix-like operating systems have been relevant since the 1990s which function similarly to Unix: popular examples are GNU (including Linux ), FreeBSD and macOS . Unix was originally meant to be

3362-630: The added benefit of closing all connections on program exit, should the user neglect to do so. In order "to minimize the amount of code added to the basic Unix kernel ", much of the NCP code ran in a swappable user process, running only when needed. 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

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3444-465: 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

3526-435: 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 launch of the free software movement in 1983. 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

3608-492: 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

3690-496: The context of this program was stored away, and the second program in memory was given a chance to run. The process continued until all programs finished running. The use of multiprogramming was enhanced by the arrival of virtual memory and virtual machine technology, which enabled individual programs to make use of memory and operating system resources as if other concurrently running programs were, for all practical purposes, nonexistent. Multiprogramming gives no guarantee that

3772-477: The core of the Mac OS X operating system, later renamed macOS . Unix-like operating systems are widely used in modern servers , workstations , and mobile devices . 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

3854-433: The early days of computing, CPU time was expensive, and peripherals were very slow. When the computer ran a program that needed access to a peripheral, the central processing unit (CPU) would have to stop executing program instructions while the peripheral processed the data. This was usually very inefficient. Multiprogramming is a computing technique that enables multiple programs to be concurrently loaded and executed into

3936-489: The entire environment unacceptably fragile. Preemptive multitasking allows the computer system to more reliably guarantee to each process a regular "slice" of operating time. It also allows the system to deal rapidly with important external events like incoming data, which might require the immediate attention of one or another process. Operating systems were developed to take advantage of these hardware capabilities and run multiple processes preemptively. Preemptive multitasking

4018-546: 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 OpenVMS 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

4100-679: 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

4182-484: The idea that the most efficient way for cooperating processes to exchange data would be to share their entire memory space. Thus, threads are effectively processes that run in the same memory context and share other resources with their parent processes , such as open files. Threads are described as lightweight processes because switching between threads does not involve changing the memory context. While threads are scheduled preemptively, some operating systems provide

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4264-415: 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 much PDP-11 specific code, and was not suitable for porting. The first port to another platform

4346-446: The language, development methodology, and individual engineer, often used for a discrete task, like a debugger or profiler. Tools may be discrete programs, executed separately – often from the command line – or may be parts of a single large program, called an integrated development environment (IDE). In many cases, particularly for simpler use, simple ad hoc techniques are used instead of a tool, such as print debugging instead of using

4428-476: 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, which in turn led to Unix fragmenting into multiple, similar — but often slightly and mutually incompatible — systems including DYNIX , HP-UX , SunOS / Solaris , AIX , and Xenix . In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4 ( SVR4 ), which

4510-428: The modular design of the Unix model, sharing components is relatively common: most or all Unix and Unix-like systems include at least some BSD code, while some include GNU utilities in their distributions. Linux and BSD Unix are increasingly filling market needs traditionally served by proprietary Unix operating systems, expanding into new markets such as the consumer desktop , mobile devices and embedded devices . In

4592-442: 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 free software counterpart to Solaris developed by Sun Microsystems , which included a CDDL -licensed kernel and a primarily GNU userland. However, Oracle discontinued

4674-402: The most successful of these tools are IDEs. Modern computers are very complex and in order to productively program them, various abstractions are needed. For example, rather than writing down a program's binary representation a programmer will write a program in a programming language like C, Java or Python. Programming tools like assemblers , compilers and linkers translate a program from

4756-471: The operating system kernel, in combination with hardware mechanisms that provide supporting functionalities, such as a memory management unit (MMU). If a process attempts to access a memory location outside its memory space, the MMU denies the request and signals the kernel to take appropriate actions; this usually results in forcibly terminating the offending process. Depending on the software and kernel design and

4838-473: The operating system should provide a set of simple tools, each of which performs a limited, well-defined function. A unified and inode -based filesystem and an inter-process communication mechanism known as " pipes " serve as the main means of communication, and a shell scripting and command language (the Unix shell ) is used to combine the tools to perform complex workflows. In the early 1990s, AT&T sold its rights in Unix to Novell , which then sold

4920-503: 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 easily be combined to perform more complicated ad hoc tasks. The focus on text and bytes made

5002-486: The overall program. A processor intended for use with multitasking operating systems may include special hardware to securely support multiple tasks, such as memory protection , and protection rings that ensure the supervisory software cannot be damaged or subverted by user-mode program errors. The term "multitasking" has become an international term, as the same word is used in many other languages such as German, Italian, Dutch, Romanian, Czech, Danish and Norwegian. In

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5084-598: 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. In May 1975, RFC 681 described the development of Network Unix by the Center for Advanced Computation at the University of Illinois Urbana-Champaign . The Unix system

5166-588: The related business operations to Santa Cruz Operation (SCO). Whether Novell also sold the copyrights to the actual software was the subject of a federal lawsuit in 2006, 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

5248-518: The running process hits a point where it has to wait for some portion of memory to be reloaded from secondary storage. Processes that are entirely independent are not much trouble to program in a multitasking environment. Most of the complexity in multitasking systems comes from the need to share computer resources between tasks and to synchronize the operation of co-operating tasks. Various concurrent computing techniques are used to avoid potential problems caused by multiple tasks attempting to access

5330-482: The same resource or device simultaneously. To mediate such access, the kernel has special rights, reflected in the distinction of kernel space from user space , the latter being a lower priority realm where most application programs operate. The origins of Unix date back to the mid-1960s when the Massachusetts Institute of Technology , Bell Labs , and General Electric were developing Multics ,

5412-476: The same resource. Bigger systems were sometimes built with a central processor(s) and some number of I/O processors , a kind of asymmetric multiprocessing . Over the years, multitasking systems have been refined. Modern operating systems generally include detailed mechanisms for prioritizing processes, while symmetric multiprocessing has introduced new complexities and capabilities. Programming tool A programming tool or software development tool

5494-535: 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 GNU operating system, many GNU packages – such as

5576-427: 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

5658-653: 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 , but was soon rewritten in C , a high-level programming language . Although this followed the lead of CTSS , Multics and Burroughs MCP , 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

5740-805: The specific error in question, the user may receive an access violation error message such as "segmentation fault". In a well designed and correctly implemented multitasking system, a given process can never directly access memory that belongs to another process. An exception to this rule is in the case of shared memory; for example, in the System V inter-process communication mechanism the kernel allocates memory to be mutually shared by multiple processes. Such features are often used by database management software such as PostgreSQL. Inadequate memory protection mechanisms, either due to flaws in their design or poor implementations, allow for security vulnerabilities that may be potentially exploited by malicious software. Use of

5822-418: 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

5904-459: 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

5986-533: Was a port of Version 6, made four years later (1977) at the University of Wollongong for the Interdata 7/32 , followed by a Bell Labs port of Version 7 to the Interdata 8/32 during 1977 and 1978. 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 Urbana–Champaign (UIUC) Department of Computer Science. During

6068-429: Was commonly used on minicomputers and mainframes from the 1970s onwards. It distinguished itself from its predecessors as the first portable operating system: almost the entire operating system is written in the C programming language , which allows Unix to operate on numerous platforms. Unix systems are characterized by a modular design that is sometimes called the " Unix philosophy ". According to this philosophy,

6150-405: Was dedicated to their use, while behind the scenes the computer is serving many users by multitasking their individual programs. In multiprogramming systems, a task runs until it must wait for an external event or until the operating system's scheduler forcibly swaps the running task out of the CPU. Real-time systems such as those designed to control industrial robots, require timely processing;

6232-473: Was eventually supported by many computer operating systems , is known today as cooperative multitasking. Although it is now rarely used in larger systems except for specific applications such as CICS or the JES2 subsystem, cooperative multitasking was once the only scheduling scheme employed by Microsoft Windows and classic Mac OS to enable multiple applications to run simultaneously. Cooperative multitasking

6314-647: Was implemented in the PDP-6 Monitor and Multics in 1964, in OS/360 MFT in 1967, and in Unix in 1969, and was available in some operating systems for computers as small as DEC's PDP-8; it is a core feature of all Unix-like operating systems, such as Linux , Solaris and BSD with its derivatives , as well as modern versions of Windows. At any specific time, processes can be grouped into two categories: those that are waiting for input or output (called " I/O bound "), and those that are fully utilizing

6396-725: Was in the design of real-time computing systems, where there are a number of possibly unrelated external activities needed to be controlled by a single processor system. In such systems a hierarchical interrupt system is coupled with process prioritization to ensure that key activities were given a greater share of available process time . As multitasking greatly improved the throughput of computers, programmers started to implement applications as sets of cooperating processes (e. g., one process gathering input data, one process processing input data, one process writing out results on disk). This, however, required some tools to allow processes to efficiently exchange data. Threads were born from

6478-402: Was one of the key reasons it emerged as an important teaching and learning tool and has had a broad influence. See § Impact , below. 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

6560-573: 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 System 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 . Because of

6642-516: Was said to "present several interesting capabilities as an ARPANET mini-host". At the time, Unix required a license from Bell Telephone Laboratories that cost US$ 20,000 for non-university institutions, while universities could obtain a license for a nominal fee of $ 150. It was noted that Bell was "open to suggestions" for an ARPANET-wide license. The RFC specifically mentions that Unix "offers powerful local processing facilities in terms of user programs, several compilers , an editor based on QED ,

6724-403: Was subsequently adopted by many commercial Unix vendors. In the 1990s, Unix and Unix-like systems grew in popularity and became the operating system of choice for over 90% of the world's top 500 fastest supercomputers , 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

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