An operating system (OS) is software, consisting of programs and data, that runs on computersand manages computer hardware resources[1] and provides common services for efficient execution of various application software.
For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between application programs and the computer hardware,[2][3] although the application code is usually executed directly by the hardware, but will frequently call the OS or be interrupted by it. Operating systems are found on almost any device that contains a computer—from cellular phones and video game consoles to supercomputers and web servers.
Examples of popular modern operating systems for personal computers are Microsoft Windows,Mac OS X, and GNU/Linux.
Early computers were built to perform a series of single tasks, like a calculator. Operating systems did not exist in their modern and more complex forms until the early 1960s.[5] Some operating system features were developed in the 1950s, such as monitor programs that could automatically run different application programs in succession to speed up processing. Hardware features were added that enabled use of runtime libraries, interrupts, and parallel processing. When personal computers by companies such as Apple Inc., Atari,IBM and Amiga became popular in the 1980s, vendors added operating system features that had previously become widely used on mainframe and mini computers. Later, many features such as graphical user interface were developed specifically for personal computer operating systems.
An operating system consists of many parts. One of the most important components is the kernel, which controls low-level processes that the average user usually cannot see: it controls how memory is read and written, the order in which processes are executed, how information is received and sent by devices like the monitor, keyboard and mouse, and decides how to interpret information received from networks. The user interface is a component that interacts with the computer user directly, allowing them to control and use programs. The user interface may be graphical with icons and a desktop, or textual, with a command line. Application programming interfaces provide services and code libraries that let applications developers write modular code reusing well defined programming sequences in user space libraries or in the operating system itself. Which features are considered part of the operating system is defined differently in various operating systems. For example, Microsoft Windows considers its user interface to be part of the operating system, while many versions of Linux do not.
In the early 1950s, a computer could execute only one program at a time. Each user had sole use of the computer and would arrive at a scheduled time with program and data on punched paper cards and tape. The program would be loaded into the machine, and the machine would be set to work until the program completed or crashed. Programs could generally be debugged via a front panel using toggle switches and panel lights. It is said thatAlan Turing was a master of this on the early Manchester Mark 1 machine, and he was already deriving the primitive conception of an operating system from the principles of the Universal Turing machine.[citation needed]
Later machines came with libraries of software, which would be linked to a user's program to assist in operations such as input and output and generating computer code from human-readable symbolic code. This was the genesis of the modern-day operating system. However, machines still ran a single job at a time. At Cambridge University in England the job queue was at one time a washing line from which tapes were hung with different colored clothes-pegs to indicate job-priority.[citation needed]
[edit]Mainframes
For more details on IBM mainframe operating systems, see History of IBM mainframe operating systems.
Through the 1950s, many major features were pioneered in the field of operating systems, including batch processing, input/output interrupt, buffering, multitasking, spooling, runtime libraries, link-loading, and programs forsorting records in files. These features were included or not included in application software at the option of application programmers, rather than in a separate operating system used by all applications. In 1959 the SHARE Operating System was released as an integrated utility for the IBM 704, and later in the 709 and 7090 mainframes.
During the 1960s, IBM's OS/360 introduced the concept of a single OS spanning an entire product line, which was crucial for the success of the System/360 machines. IBM's current mainframe operating systems are distant descendants of this original system and applications written for OS/360 can still be run on modern machines.[citation needed] In the mid-'70s, MVS, a descendant of OS/360, offered the first[citation needed] implementation of using RAM as a transparent cache for data.
OS/360 also pioneered the concept that the operating system keeps track of all of the system resources that are used, including program and data space allocation in main memory and file space in secondary storage, and file locking during update. When the process is terminated for any reason, all of these resources are re-claimed by the operating system.
The alternative CP-67 system for the S/360-67 started a whole line of IBM operating systems focused on the concept of virtual machines. Other operating systems used on IBM S/360 series mainframes included systems developed by IBM: COS/360 (Compatabililty Operating System), DOS/360 (Disk Operating System), TSS/360 (Time Sharing System), TOS/360 (Tape Operating System), BOS/360 (Basic Operating System), and ACP (Airline Control Program), as well as a few non-IBM systems: MTS (Michigan Terminal System) and MUSIC (Multi-User System for Interactive Computing).
Control Data Corporation developed the SCOPE operating system in the 1960s, for batch processing. In cooperation with the University of Minnesota, the KRONOS and later the NOS operating systems were developed during the 1970s, which supported simultaneous batch and timesharing use. Like many commercial timesharing systems, its interface was an extension of the Dartmouth BASIC operating systems, one of the pioneering efforts in timesharing and programming languages. In the late 1970s, Control Data and the University of Illinois developed the PLATO operating system, which used plasma panel displays and long-distance time sharing networks. Plato was remarkably innovative for its time, featuring real-time chat, and multi-user graphical games. Burroughs Corporationintroduced the B5000 in 1961 with the MCP, (Master Control Program) operating system. The B5000 was a stack machine designed to exclusively support high-level languages with no machine language or assembler, and indeed the MCP was the first OS to be written exclusively in a high-level language – ESPOL, a dialect of ALGOL. MCP also introduced many other ground-breaking innovations, such as being the first commercial implementation of virtual memory. During development of the AS400, IBM made an approach to Burroughs to licence MCP to run on the AS400 hardware. This proposal was declined by Burroughs management to protect its existing hardware production. MCP is still in use today in the Unisys ClearPath/MCP line of computers.
UNIVAC, the first commercial computer manufacturer, produced a series of EXEC operating systems. Like all early main-frame systems, this was a batch-oriented system that managed magnetic drums, disks, card readers and line printers. In the 1970s, UNIVAC produced the Real-Time Basic (RTB) system to support large-scale time sharing, also patterned after the Dartmouth BC system.
General Electric and MIT developed General Electric Comprehensive Operating Supervisor (GECOS), which introduced the concept of ringed security privilege levels. After acquisition by Honeywell it was renamed to General Comprehensive Operating System (GCOS).
Digital Equipment Corporation developed many operating systems for its various computer lines, including TOPS-10 and TOPS-20 time sharing systems for the 36-bit PDP-10 class systems. Prior to the widespread use of UNIX, TOPS-10 was a particularly popular system in universities, and in the early ARPANET community.
In the late 1960s through the late 1970s, several hardware capabilities evolved that allowed similar or ported software to run on more than one system. Early systems had utilized microprogramming to implement features on their systems in order to permit different underlying architecture to appear to be the same as others in a series. In fact most 360's after the 360/40 (except the 360/165 and 360/168) were microprogrammed implementations. But soon other means of achieving application compatibility were proven to be more significant.
The enormous investment in software for these systems made since 1960s caused most of the original computer manufacturers to continue to develop compatible operating systems along with the hardware. The notable supported mainframe operating systems include:
- Burroughs MCP – B5000, 1961 to Unisys Clearpath/MCP, present.
- IBM OS/360 – IBM System/360, 1966 to IBM z/OS, present.
- IBM CP-67 – IBM System/360, 1967 to IBM z/VM, present.
- UNIVAC EXEC 8 – UNIVAC 1108, 1967, to OS 2200 Unisys Clearpath Dorado, present.
Example of OS:
Microsoft Windows
Microsoft Windows is a family of proprietary operating systems most commonly used on personal computers. It is the most common family of operating systems for the personal computer, with about 90% of the market share.[6][7][8] Currently, the most widely used version of the Windows family is Windows XP,[9] released on October 25, 2001. The newest version is Windows 7 for personal computers and Windows Server 2008 R2 for servers.
Microsoft Windows originated in 1981 as an add-on to the older MS-DOS operating system for the IBM PC. First publicly released in 1985, Windows came to dominate the business world of personal computers, and went on to set a number of industry standards and commonplace applications[POV? ]. Beginning with Windows XP, all modern versions are based on the Windows NT kernel. Current versions of Windows run on IA-32 and x86-64 processors, although older versions sometimes supported other architectures.
Windows is also used on servers, supporting applications such as web servers anddatabase servers. In recent years, Microsoft has spent significant marketing and research & development money to demonstrate that Windows is capable of running any enterprise application, which has resulted in consistent price/performance records (see the TPC) and significant acceptance in the enterprise market. However, its usage in servers is not as widespread as personal computers, and here Windows actively competes against Linux and BSD for market share, while still capturing a steady majority by some accounts.[10][11]
[edit]Unix and Unix-like operating systems
Main article: Unix
Ken Thompson wrote B, mainly based on BCPL, which he used to write Unix, based on his experience in the MULTICS project. B was replaced by C, and Unix developed into a large, complex family of inter-related operating systems which have been influential in every modern operating system (see History). The Unix-like family is a diverse group of operating systems, with several major sub-categories includingSystem V, BSD, and GNU/Linux. The name "UNIX" is a trademark of The Open Groupwhich licenses it for use with any operating system that has been shown to conform to their definitions. "Unix-like" is commonly used to refer to the large set of operating systems which resemble the original Unix.
Unix-like systems run on a wide variety of machine architectures. They are used heavily for servers in business, as well as workstations in academic and engineering environments. Free Unix variants, such asGNU/Linux and BSD, are popular in these areas.
Some Unix variants like HP's HP-UX and IBM's AIX are designed to run only on that vendor's hardware. Others, such as Solaris, can run on multiple types of hardware, including x86 servers and PCs. Apple's Mac OS X, a hybrid kernel-based BSD variant derived fromNeXTSTEP, Mach, and FreeBSD, has replaced Apple's earlier (non-Unix) Mac OS.
Unix interoperability was sought by establishing the POSIX standard. The POSIX standard can be applied to any operating system, although it was originally created for various Unix variants.
[edit]BSD and its descendants
Main article: Berkeley Software Distribution
A subgroup of the Unix family is the Berkeley Software Distribution family, which includes FreeBSD, NetBSD, and OpenBSD. These operating systems are most commonly found on webservers, although they can also function as a personal computer OS. The Internet owes much of its existence to BSD, as many of the protocols now commonly used by computers to connect, send and receive data over a network were widely implemented and refined in BSD. The world wide web was also first demonstrated on a number of computers running an OS based on BSD calledNextStep.
BSD has its roots in Unix. In 1974, University of California, Berkeley installed its first Unix system. Over time, students and staff in the computer science department there began adding new programs to make things easier, such as text editors. When Berkely received new VAX computers in 1978 with Unix installed, the school's undergraduates modified Unix even more in order to take advantage of the computer's hardware possibilities. The Defense Advanced Research Projects Agency of the US Department of Defense took interest, and decided to fund the project. Many schools, corporations, and government organizations took notice and started to use Berkeley's version of Unix instead of the official one distributed by AT&T. Steve Jobs, upon leaving Apple Inc. in 1985, formed NeXT Inc., a company that manufactured high-end computers running on a variation of BSD called NeXTSTEP. One of these computers was used by Tim Berners-Lee as the first webserver to create the World Wide Web.
Developers like Keith Bostic encouraged the project to replace any non-free code that originated with Bell Labs. Once this was done, however, AT&T sued. Eventually, after two years of legal disputes, the BSD project came out ahead and spawned a number of free derivatives, such as FreeBSD and NetBSD. In this two year wait, GNU and Linux appeared.
[edit]Mac OS X
Main article: Mac OS X
Mac OS X is a line of partially proprietary graphical operating systems developed, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currently shipping Macintosh computers. Mac OS X is the successor to the original Mac OS, which had been Apple's primary operating system since 1984. Unlike its predecessor, Mac OS X is a UNIX operating system built on technology that had been developed atNeXT through the second half of the 1980s and up until Apple purchased the company in early 1997.
The operating system was first released in 1999 as Mac OS X Server 1.0, with a desktop-oriented version (Mac OS X v10.0) following in March 2001. Since then, six more distinct "client" and "server" editions of Mac OS X have been released, the most recent being Mac OS X v10.6, which was first made available on August 28, 2009. Releases of Mac OS X are named after big cats; the current version of Mac OS X is "Snow Leopard".
The server edition, Mac OS X Server, is architecturally identical to its desktop counterpart but usually runs on Apple's line of Macintoshserver hardware. Mac OS X Server includes work group management and administration software tools that provide simplified access to key network services, including a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others.
[edit]Plan 9
Ken Thompson, Dennis Ritchie and Douglas McIlroy at Bell Labs designed and developed the C programming language to build the operating system Unix. Programmers at Bell Labs went on to develop Plan 9 and Inferno, which were engineered for modern distributed environments. Plan 9 was designed from the start to be a networked operating system, and had graphics built-in, unlike Unix, which added these features to the design later. It is currently released under the Lucent Public License. Inferno was sold to Vita Nuova Holdings and has been released under a GPL/MIT license.
[edit]Linux and GNU
Linux is the generic name for a UNIX-like operating system that can be used on a wide range of devices from supercomputers to wristwatches. The Linux kernel is released under an open source license, so anyone can read and modify its code. It has been modified to run on a large variety of electronics. Although estimates suggest it is used on only 0.5-2% of all personal computers,[8] it has been widely adopted for use in servers and embedded systems[12][13] (such as cell phones). Linux has superseded Unix in most places[which?], and is used on the 10 most powerful supercomputers in the world.[14]
The GNU project is a mass collaboration of programmers who seek to create a completely free and open operating system that was similar to Unix but with completely original code. It was started in 1983 by Richard Stallman, and is responsible for many of the parts of most Linux variants. For this reason, Linux is often called GNU/Linux. Thousands of pieces of software for virtually every operating system are licensed under the GNU General Public License. Meanwhile, the Linux kernel began as a side project of Linus Torvalds, a university student from Finland. In 1991, Torvalds began work on it, and posted information about his project on a newsgroup for computer students and programmers. He received a wave of support and volunteers who ended up creating a full-fledged kernel. Programmers from GNU took notice, and members of both projects worked to integrate the finished GNU parts into the linux kernel in order to create a full-fledged operating system.
[edit]Google Chrome OS
Main article: Google Chrome OS
Chrome is an operating system based on the Linux kernel and designed by Google. Chrome targets computer users who spend most of their time on the Internet—it is technically only a web browser with no other applications, and relies on Internet applications used in the web browser to accomplish tasks such as word processing and media viewing.
[edit]Other
Older operating systems which are still used in niche markets include OS/2 from IBM and Microsoft; Mac OS, the non-Unix precursor to Apple's Mac OS X; BeOS; XTS-300. Some, most notably Haiku, RISC OS, MorphOS, AmigaOS 4 and FreeMint continue to be developed as minority platforms for enthusiast communities and specialist applications. OpenVMS formerly from DEC, is still under active development by Hewlett-Packard. Yet other operating systems are used almost exclusively in academia, for operating systems education or to do research on operating system concepts. A typical example of a system that fulfills both roles is MINIX, while for example Singularity is used purely for research.
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