Operating system
An operating system is a special computer program that manages the relationship between application software, the wide variety of hardware that makes up a computer system, and the user of the system.
The lowest level of any operating system is its kernel, the first layer of software loaded into computer memory when a system boots, or starts up. The kernel then provides access to various common core services to all other system and application programs. These services include, but are not limited to: disk access, memory management, task scheduling, and access to other hardware devices.
As well as the kernel, an operating system is often distributed with tools for programs to display and manage a graphical user interface, as well as utility programs for tasks such as managing files and configuring the operating system. They are also often distributed with application software that does not relate directly to the operating system's core function, but which the operating system distributor finds advantageous to supply with the operating system. The exact delineation between the operating system and application software is not precise, and is occasionally subject to controversy. For example, one of the key questions in the United States v. Microsoft antitrust trial was whether Microsoft's Internet Explorer web browser was part of its Windows operating system or if it was a separable piece of application software.
Like the term "operating system" itself, the question of what exactly should form the "kernel" is subject to some controversy, with debates over whether things like file systems should be included in the kernel. Various camps advocate microkernels, monolithic kernels, and so on as compromises.
Operating systems are used on many, but by no means all computer systems. The simplest computers, including the smallest embedded systems and many of the first computers did not have operating systems, and relied on the application programmer to manage the minimal hardware themselves, perhaps with the aid of libraries developed for the purpose. Commercially-supplied operating systems are present on virtually all modern devices described as computers, from personal computers to mainframes, as well as mobile computers such as PDAs and mobile phones.
Contents
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* 1 History of operating systems
* 2 Today's operating systems
o 2.1 Unix-like systems
o 2.2 Microsoft Windows
o 2.3 Other operating systems
* 3 See also
o 3.1 General topics
o 3.2 Other topics
* 4 External links
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History of operating systems
Main article: History of operating systems
The first computers did not have operating systems. However, software tools for managing the system and simplifying the use of hardware appeared very quickly afterwards, and gradually expanded in scope. By the early 1960s, commercial computer vendors were supplying quite extensive tools for streamlining the development, scheduling, and execution of jobs on batch processing systems. Examples were produced by UNIVAC and Control Data Corporation, amongst others.
Through the 1960's, several major concepts drove the development of operating systems. They included the development of the IBM System/360, a family of mainframe computers available in widely differing capacities and price points, for which a single operating system OS/360 was developed. IBM's current mainframe operating systems are distant descendants of this original system, and indeed applications written for the OS/360 can still be run on modern machines. OS/360 also contained another important advance, being tied to the development of the hard disk permanent storage device. Another key development was the concept of time-sharing; the idea of sharing the resources of expensive computers amongst multiple computer users interacting in real time with the system, who would all have the illusion of having their own personal computer; the Multics timesharing system was the most famous of a number of new operating systems developed to take advantage of the concept.
Multics, particularly, was an inspiration to a number of operating systems developed in the 1970's, notably Unix. Another commercially-popular minicomputer operating system was VMS.
The first microcomputers did not have the capacity or need for the elaborate operating systems that had been developed for mainframes and minis; minimalistic operating systems were developed. One notable early operating system was CP/M, which was supported on many early microcomputers and was largely cloned in creating MS-DOS, which became wildly popular as the operating system chosen for the IBM PC, its successors making Microsoft one of the world's most profitable companies. The major alternative throughout the 1980s in the microcomputer market was Mac OS, tied intimately to the Apple Macintosh computer.
By the 1990's, the microcomputer had evolved to the point where, as well as extensive GUI facilities, the robustness and flexibility of operating systems of larger computers became increasingly desirable. Microsoft's response to this change was the development of Windows NT, which now serves as the basis for Microsoft's entire operating system line. Apple rebuilt their operating system on top of a Unix core as Mac OS X. Initially hobbyist-developed reimplementations of Unix, assembled with the assistance of tools from the GNU project, also became popular as the decade passed; versions based on the the Linux kernel are by far the most popular.
The growing complexity of embedded devices has a growing trend to use embedded operating systems on them.
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Today's operating systems
Command line interface (or CLI) OS's such as DOS, use only the keyboard for input. Modern OS's use a mouse for input with a graphical user interface (GUI) sometimes implemented as a shell. The appropriate OS may depend on the hardware architecture, specifically the CPU, with only Linux and BSD running on almost any CPU. Since the early 1990's the choice for personal computers has been largely limited to the Microsoft Windows family and the Unix-like family, of which Linux is becoming the major representative. Mainframe computers and embedded systems use a variety of different operating systems, many with no direct connection to Windows or Unix, but typically more similar to Unix than Windows.
* Personal computers
o IBM PC compatible - smaller Unix-variants, like Linux and BSD, and Microsoft Windows
o Apple Macintosh - Mac OS X, Linux and BSD
* Mainframes - A number of unique OS's, sometimes Linux and other Unix variants.
* Embedded systems - a variety of dedicated OS's, and limited versions of Linux or other OS's
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Unix-like systems
The Unix-like family is a diverse group of operating systems, with several major sub-categories including System V, BSD, and Linux. The name "Unix" is a trademark of The Open Group which licenses it for use to any operating system that has been shown to conform to the definitions that they have cooperatively developed. The name is commonly used to refer to the large set of operating systems which resemble the original Unix.
Unix systems run on a wide variety of machine architectures. They are used heavily as server systems in business, as well as workstations in academic and engineering environments. Free software Unix variants, such as Linux and BSD, are increasingly popular. They have made inroads on the desktop market as well, particularly with "user-friendly" Linux distributions such as Ubuntu Linux.
Some Unix variants like HP's HP-UX and IBM's AIX are designed to run only on that vendor's proprietary hardware. Others, such as Solaris, can run on both proprietary hardware and on commodity x86 PCs. Apple's Mac OS X, a BSD variant derived from NeXTSTEP and FreeBSD, has replaced Apple's earlier (non-Unix) Mac OS in a small but dedicated market, in the process becoming the most popular proprietary Unix system.
Over the past several years, free Unix systems have supplanted proprietary ones in many markets. For instance, scientific modeling and computer animation were once the province of SGI's IRIX. Today, they are dominated by Linux-based or Plan 9 clusters.
The team at Bell Labs who designed and developed Unix, went on to develop Plan 9 and Inferno which implemented what Unix had only envisioned. They had graphics and networking built-in, unlike Unix counterparts that added them to the design later. Plan 9 did not become popular because unlike many Unix distributions, it was not originally free. It is now released under Lucent Public License, and has an expanding community of developers.
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Microsoft Windows
The Microsoft Windows family of operating systems originated as a graphical layer on top of the older MS-DOS environment for the IBM PC. Modern versions are based on the newer Windows NT core that first took shape in OS/2 and the kernel also borrows from OpenVMS. Windows runs on 32- and 64-bit Intel and AMD computers, although earlier versions also ran on the DEC Alpha, MIPS and PowerPC architectures (and there was work in progress to make it work also on the SPARC architecture).
Today Windows enjoys a near-monopoly of around 90% of the worldwide desktop market share. [1] It is also used on low-end and mid-range servers, supporting applications such as web servers and database servers. In recent years, Microsoft has spent significant marketing and R&D money to demonstrate that Windows is capable of running any enterprise application (see the TPC article).
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Other operating systems
Mainframe operating systems, such as IBM's z/OS, and embedded operating systems such as QNX, eCos, and PalmOS, are usually unrelated to Unix and Windows, except Windows CE, Windows NT Embedded 4.0 and Windows XP Embedded which are related to Windows and several *BSDs and Linux distributions tailored for the requirements of an embedded system. OpenVMS from Hewlett-Packard (formerly DEC), is still under active development.
Older operating systems which are still used in niche markets include the Windows-like OS/2 from IBM; Mac OS, the non-Unix precursor to Apple's Mac OS X; RISC OS, which is specifically designed to run on ARM processor architectures; and AmigaOS, the first graphical user interface (GUI) based operating system with advanced multimedia capabilities available to the general public.
Research and development of new kinds of operating systems is an active subfield of computer science. Microsoft Singularity is a research project to develop an operating system with better memory protection
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