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Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed, both commercially and non-commercially, by anyone under licenses such as the GNU General Public License.
Typically Linux is packaged in a format known as a Linux distribution for desktop and server use. Linux distributions include the Linux kernel and all of the supporting software required to run a complete system, such as utilities and libraries, the X Window System, the GNOME and KDE desktop environments, and the Apache HTTP Server. Commonly-used applications with desktop Linux systems include the Mozilla Firefox web-browser and the OpenOffice.org office application suite.
Linux can be installed on a wide variety of computer hardware, ranging from embedded devices such as mobile phones and wristwatches to mainframes and supercomputers. Linux is predominantly known for its use in servers; in 2007 Linux's overall share of the server market was estimated at 12.7%, while a 2008 estimate suggested that 60% of all web servers ran Linux. Most desktop computers run either Mac OS X or Microsoft Windows, with Linux having only 1-2% of the desktop market. However, desktop use of Linux has become increasingly popular in recent years, partly owing to the popular Ubuntu distribution and the emergence of netbooks.
The name "Linux" comes from the Linux kernel, originally written in 1991 by Linus Torvalds.
A Linux-based system is a modular Unix-like operating system. It derives much of its basic design from principles established in Unix during the 1970s and 1980s. Such a system uses a monolithic kernel, the Linux kernel, which handles process control, networking, and peripheral and file system access. Device drivers are integrated directly with the kernel.
Separate projects that interface with the kernel provide much of the system's higher-level functionality. The GNU user land is an important part of most Linux-based systems, providing the most common implementation of the C library, a popular shell, and many of the common Unix tools which carry out many basic operating system tasks. The graphical user interface (or GUI) used by most Linux systems is based on the X Window System.
Users can control a Linux-based system through a command line interface (or CLI), a graphical user interface (or GUI), or through controls attached to the associated hardware (this is common for embedded systems). For desktop systems, the default mode is usually graphical user interface, where the CLI is available through terminal emulator windows or on a separate virtual console.
A Linux system typically provides a CLI through a shell, which is the traditional way of interacting with a UNIX system. A Linux distribution specialized for servers may use the CLI as its only interface. A headless system that runs without even a monitor can be controlled by the command line via a remote-control protocol such as SSH or telnet.
Most low-level Linux components, including the GNU user land, use the CLI exclusively. The CLI is particularly suited for automation of repetitive or delayed tasks, and provides very simple inter-process communication. A graphical terminal emulator program is often used to access the CLI from a Linux desktop.
A summarized history of Unix-like operating systems showing Linux's origins. Note that despite similar architectural designs and concepts being shared as part of the POSIX standard, Linux does not share any non-free source code with the original Unix or MINIX.
The primary difference between Linux and many other popular contemporary operating systems is that the Linux kernel and other components are free and open source software. Linux is not the only such operating system, although it is by far the most widely used. Some free and open source software licenses are based on the principle of copy left, a kind of reciprocity: any work derived from a copy left piece of software must also be copy left itself.
Free software projects, although developed in a collaborative fashion, are often produced independently of each other. The fact that the software licenses explicitly permit redistribution, however, provides a basis for larger scale projects that collect the software produced by stand-alone projects and make it available all at once in the form of a Linux distribution.
A Linux distribution, commonly called a "distro", is a project that manages a remote collection of system software and application software packages available for download and installation through a network connection. This allows the user to adapt the operating system to his/her specific needs. Distributions are maintained by individuals, loose-knit teams, volunteer organizations, and commercial entities. A distribution is responsible for the default configuration of the installed Linux kernel, general system security, and more generally integration of the different software packages into a coherent whole. Distributions typically use a package manager such as Synaptic or YAST to install, remove and update all of a system's software from one central location.
As well as those designed for general purpose use on desktops and servers, distributions may be specialized for different purposes including: computer architecture support, embedded systems, stability, security, localization to a specific region or language, targeting of specific user groups, support for real-time applications, or commitment to a given desktop environment. Furthermore, some distributions deliberately include only free software.
Linux is a widely ported operating system kernel. The Linux kernel runs on a highly diverse range of computer architectures: in the hand-held ARM-based iPAQ and the mainframe IBM System z9, System z10 in devices ranging from mobile phones to supercomputers. Specialized distributions exist for less mainstream architectures. The ELKS kernel fork can run on Intel 8086 or Intel 80286 16-bit microprocessors, while the ÂµClinux kernel fork may run on systems without a memory management unit. The kernel also runs on architectures that were only ever intended to use a manufacturer-created operating system, such as Macintosh computers (with both PowerPC and Intel processors), PDAs, video game consoles, portable music players, and mobile phones.
Mac OS is the trademarked name for a series of graphical user interface-based operating systems developed by Apple Inc. (formerly Apple Computer, Inc.) for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface. The original form of what Apple would later name the "Mac OS" was the integral and unnamed system software first introduced in 1984 with the original Macintosh, usually referred to simply as the System software.
Apple deliberately downplayed the existence of the operating system in the early years of the Macintosh to help make the machine appear more user-friendly and to distance it from other operating systems such as MS-DOS, which was more arcane and technically challenging. Much of this early system software was held in ROM, with updates typically provided free of charge by Apple dealers on floppy disk. As increasing disk storage capacity and performance gradually eliminated the need for fixing much of an advanced GUI operating system in ROM, Apple explored cloning while positioning major operating system upgrades as separate revenue-generating products, first with System 7.1 and System 7.5, then with Mac OS 7.6 in 1997.
Early versions of the Mac OS were compatible only with Motorola 68000-based Macintoshes. As Apple introduced computers with PowerPC hardware, the OS was upgraded to support this architecture as well. Mac OS 8.1 was the last version that could run on a 68000-class processor (the 68040). Mac OS X, which has superseded the "Classic" Mac OS, is compatible with both PowerPC and Intel processors through version 10.5 ("Leopard"). Version 10.6 ("Snow Leopard") supports only Intel processors.
Mac OS X is the tenth major version of Apple's operating system for Macintosh computers. Previous Macintosh operating systems were named using Arabic numerals, e.g. Mac OS 8 and Mac OS 9. The letter X in Mac OS X's name refers to the number 10, a Roman numeral. It is therefore correctly pronounced "ten" in this context, though "X" is also a common pronunciation Mac OS X's core is a POSIX compliant operating system (OS) built on top of the XNU kernel, with standard Unix facilities available from the command line interface. Apple released this family of software as a free and open source operating system named Darwin, but it later became partially proprietary. On top of Darwin, Apple layered a number of components, including the Aqua interface and the Finder, to complete the GUI-based operating system which is Mac OS X.
Mac OS X introduced a number of new capabilities to provide a more stable and reliable platform than its predecessor, Mac OS 9. For example, pre-emptive multitasking and memory protection improved the system's ability to run multiple applications simultaneously without them interrupting or corrupting each other. Many aspects of Mac OS X's architecture are derived from Open step, which was designed to be portable, to ease the transition from one platform to another. For example, Next step was ported from the original 68k-based NeXT workstations to x86 and other architectures before NeXT was purchased by Apple, and Open Step was later ported to the PowerPC architecture as part of the Rhapsody project.
Mac OS X Architecture implements a layered framework. The layered framework aids rapid development of applications by providing existing code for common tasks.
Mac OS X includes its own software development tools, most prominently an integrated development environment called Xcode. Xcode provides interfaces to compilers that support several programming languages including C, C++, Objective-C, and Java. For the Apple Intel Transition, it was modified so that developers could build their applications as a universal binary, which provides compatibility with both the Intel-based and PowerPC-based Macintosh lines.
One of the major differences between the previous versions of Mac OS and OS X was the addition of the Aqua GUI, a graphical user interface with water-like elements. Every window element, text, graphics, or widgets is drawn on-screen using the anti-aliasing technology. ColorSync, a technology introduced many years before, was improved and built into the core drawing engine, to provide color matching for printing and multimedia professionals. Also, drop shadows were added around windows and isolated text elements to provide a sense of depth. New interface elements were integrated, including sheets (document modal dialog boxes attached to specific windows) and drawers.
Apple has continued to change aspects of the OS X appearance and design, particularly with tweaks to the appearance of windows and the menu bar. One example of a UI behavioral change is that previewed video and audio files no longer have progress bars in column view; instead, they have mouse-over start and stop buttons as of 10.5.
The human interface guidelines published by Apple for Mac OS X are followed by many applications, giving them consistent user interface and keyboard shortcuts. In addition, new services for applications are included, which include spelling and grammar checkers, special characters palette, color picker, font chooser and dictionary; these global features are present in every Cocoa application, adding consistency. The graphics system OpenGL composites windows onto the screen to allow hardware-accelerated drawing. This technology, introduced in version 10.2, is called Quartz Extreme, a component of Quartz. Quartz's internal imaging model correlates well with the Portable Document Format (PDF) imaging model, making it easy to output PDF to multiple devices. As a side result, PDF viewing is a built-in feature.
In version 10.3, Apple added Exposé, a feature which includes three functions to help accessibility between windows and desktop. Its functions are to instantly display all open windows as thumbnails for easy navigation to different tasks, display all open windows as thumbnails from the current application, and hide all windows to access the desktop. Also, File Vault was introduced, which is an optional encryption of the user's files with Advanced Encryption Standard (AES-128).
Features introduced in version 10.4 include Automator, an application designed to create an automatic workflow for different tasks; Dashboard, a full-screen group of small applications called desktop widgets that can be called up and dismissed in one keystroke; and Front Row, a media viewer interface accessed by the Apple Remote. Moreover, the Sync Services were included, which is a system that allows applications to access a centralized extensible database for various elements of user data, including calendar and contact items. The operating system then managed conflicting edits and data consistency.
As of version 10.5, all system icons are scalable up to 512Ã-512 pixels, to accommodate various places where they appear in larger size, including for example the Cover Flow view, a three-dimensional graphical user interface included with iTunes, the Finder, and other Apple products for visually skimming through files and digital media libraries via cover artwork. This version includes Spaces, a virtual desktop implementation which enables the user to have more than one desktop and display them in an Exposé-like interface. Mac OS X v10.5 includes an automatic backup technology called Time Machine, which provides the ability to view and restore previous versions of files and application data; and Screen Sharing was built in for the first time.
Finder is a file browser allowing quick access to all areas of the computer, which has been modified throughout subsequent releases of Mac OS X. Quick Look is part of Mac OS X Leopard's Finder. It allows for dynamic previews of files, including videos and multi-page documents, without opening their parent applications. Spotlight search technology, which is integrated into the Finder since Mac OS X Tiger, allows rapid real-time searches of data files; mail messages; photos; and other information based on item properties (meta data) and/or content. Mac OS X makes use of a Dock, which holds file and folder shortcuts as well as minimized windows. Mac OS X Architecture implements a layered framework. The layered framework aids rapid development of applications by providing existing code for common tasks.
Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces (GUIs). Microsoft Windows came to dominate the world's personal computer market, overtaking Mac OS, which had been introduced previously. As of October 2009, Windows had approximately 91% of the market share of the client operating systems for usage on the Internet. The most recent client version of Windows is Windows 7; the most recent server version is Windows Server 2008 R2.
Windows OS market share
Windows Server 2003
Microsoft has taken two parallel routes in its operating systems. One route has been for the home user and the other has been for the professional IT user. The dual routes have generally led to home versions having greater multimedia support and less functionality in networking and security, and professional versions having inferior multimedia support and better networking and security.
The first version of Microsoft Windows, version 1.0, released in November 1985, lacked a degree of functionality and achieved little popularity, and was to compete with Apple's own operating system. Windows 1.0 is not a complete operating system; rather, it extends MS-DOS. Microsoft Windows version 2.0 was released in November, 1987 and was slightly more popular than its predecessor. Windows 2.03 (release date January 1988) had changed the OS from tiled windows to overlapping windows.
Microsoft Windows version 3.0, released in 1990, was the first Microsoft Windows version to achieve broad commercial success, selling 2 million copies in the first six months. It featured improvements to the user interface and to multitasking capabilities. It received a facelift in Windows 3.1, made generally available on March 1, 1992.
In July 1993, Microsoft released Windows NT based on a new kernel. NT was considered to be the professional OS and was the first Windows version to utilize preemptive multitasking. Windows NT would later be retooled to also function as a home operating system, with Windows XP.
On August 24, 1995, Microsoft released Windows 95, a new, and major, consumer version that made further changes to the user interface, and also used preemptive multitasking. Windows 95 was designed to replace not only Windows 3.1, but also Windows for Workgroups, and MS-DOS. It was also the first Windows operating system to use Plug and Play capabilities. The changes Windows 95 brought to the desktop were revolutionary, as opposed to evolutionary, such as those in Windows 98 and Windows Me.
The next in the consumer line was Microsoft Windows 98 released on June 25, 1998. It was substantially criticized for its slowness and for its unreliability compared with Windows 95, but many of its basic problems were later rectified with the release of Windows 98 Second Edition in 1999.
As part of its "professional" line, Microsoft released Windows 2000 in February 2000. The consumer version following Windows 98 was Windows Me (Windows Millennium Edition). Released in September 2000, Windows Me implemented a number of new technologies for Microsoft: most notably publicized was "Universal Plug and Play". During 2004 part of the Source Code for Windows 2000 was leaked onto the internet. This was bad for Microsoft as the same kernel used in Windows 2000 was used in Windows XP.
In October 2001, Microsoft released Windows XP, a version built on the Windows NT kernel that also retained the consumer-oriented usability of Windows 95 and its successors. This new version was widely praised in computer magazines. It shipped in two distinct editions, "Home" and "Professional", the former lacking many of the superior security and networking features of the Professional edition. Additionally, the first "Media Center" edition was released in 2002, with an emphasis on support for DVD and TV functionality including program recording and a remote control. Mainstream support for Windows XP ended on April 14, 2009. Extended support will continue until April 8, 2014.
In April 2003, Windows Server 2003 was introduced, replacing the Windows 2000 line of server products with a number of new features and a strong focus on security; this was followed in December 2005 by Windows Server 2003 R2.
On January 30, 2007 Microsoft released Windows Vista. It contains a number of new features, from a redesigned shell and user interface to significant technical changes, with a particular focus on security features. It is available in a number of different editions, and has been subject to some criticism.
Consumer versions of Windows were originally designed for ease-of-use on a single-user PC without a network connection, and did not have security features built in from the outset. However, Windows NT and its successors are designed for security (including on a network) and multi-user PCs, but were not initially designed with Internet security in mind as much, since, when it was first developed in the early 1990s, Internet use was less prevalent.
These design issues combined with programming errors (e.g. buffer overflows) and the popularity of Windows means that it is a frequent target of computer worm and virus writers. In June 2005, Bruce Schneier's Counterpane Internet Security reported that it had seen over 1,000 new viruses and worms in the previous six months.
Microsoft releases security patches through its Windows Update service approximately once a month (usually the second Tuesday of the month), although critical updates are made available at shorter intervals when necessary. In versions of Windows after and including Windows 2000 SP3 and Windows XP, updates can be automatically downloaded and installed if the user selects to do so. As a result, Service Pack 2 for Windows XP, as well as Service Pack 1 for Windows Server 2003, were installed by users more quickly than it otherwise might have been.
While the Windows 9x series offered the option of having profiles for multiple users, they had no concept of access privileges, and did not allow concurrent access; and so were not true multi-user operating systems. In addition, they implemented only partial memory protection. They were accordingly widely criticized for lack of security.
The Windows NT series of operating systems, by contrast, are true multi-user, and implement absolute memory protection. However, a lot of the advantages of being a true multi-user operating system were nullified by the fact that, prior to Windows Vista, the first user account created during the setup process was an administrator account, which was also the default for new accounts. Though Windows XP did have limited accounts, the majority of home users did not change to an account type with fewer rights - partially due to the number of programs which unnecessarily required administrator rights - and so most home users ran as administrator all the time.
Windows Vista changes this by introducing a privilege elevation system called User Account Control. When logging in as a standard user, a logon session is created and a token containing only the most basic privileges is assigned. In this way, the new logon session is incapable of making changes that would affect the entire system. When logging in as a user in the Administrators group, two separate tokens are assigned. The first token contains all privileges typically awarded to an administrator, and the second is a restricted token similar to what a standard user would receive. User applications, including the Windows Shell, are then started with the restricted token, resulting in a reduced privilege environment even under an Administrator account. When an application requests higher privileges or "Run as administrator" is clicked, UAC will prompt for confirmation and, if consent is given (including administrator credentials if the account requesting the elevation is not a member of the administrators group), start the process using the unrestricted token.
All Windows versions from Windows NT 3 have been based on a file system permission system referred to as AGLP (Accounts, Global, Local, Permissions) AGDLP which in essence where file permissions are applied to the file/folder in the form of a 'local group' which then has other 'global groups' as members. These global groups then hold other groups or users depending on different Windows versions used. This system varies from other vendor products such as Linux and NetWare due to the 'static' allocation of permission being applied directory to the file or folder. However using this process of AGLP/AGDLP/AGUDLP allows a small number of static permissions to be applied and allows for easy changes to the account groups without reapplying the file permissions on the files and folders.
On January 6, 2005, Microsoft released a Beta version of Microsoft Antispyware, based upon the previously released Giant Antispyware. On February 14, 2006, Microsoft Antispyware became Windows Defender with the release of Beta 2. Windows Defender is a freeware program designed to protect against spyware and other unwanted software. Windows XP and Windows Server 2003 users who have genuine copies of Microsoft Windows can freely download the program from Microsoft's web site, and Windows Defender ships as part of Windows Vista and 7.
Windows Mobile is a compact mobile operating system developed by Microsoft, and designed for use in smart phones and mobile devices.
It is based on Windows CE 5.2, and features a suite of basic applications developed using the Microsoft Windows API. It is designed to be somewhat similar to desktop versions of Windows, feature-wise and aesthetically. Additionally, third-party software development is available for Windows Mobile, and software can be purchased via the Windows Marketplace for Mobile.
Originally appearing as the Pocket PC 2000 operating system, most Windows Mobile phones come with a stylus pen, which is used to enter commands by tapping it on the screen. Windows Mobile has been updated multiple times, with the current version being Windows Mobile 6.5. The next major revision, Windows Mobile 7.0, is expected to be released in Q4 2010, and is also expected to make Windows Mobile a much more serious competitor to today's other mobile platforms.
Windows Mobile's share of the Smartphone market has fallen year-on-year, decreasing 20% in Q3 2009. It is the 3rd most popular smart phone operating system for business use (after BlackBerry and iPhone), with a 24% share among enterprise users. In overall sales, it is the 4th most popular smart phone operating system, with a 7.9% share of the worldwide smart phone market.
Windows Mobile for Pocket PC carries these standard features in most of its versions:
Today Screen shows the current date, owner information, upcoming appointments, e-mail messages, and tasks. (Is now Home screen in later WM6.5 builds)
The taskbar shows the current time and the volume.
Office Mobile a suite of Mobile versions of Microsoft Office applications
Outlook Mobile comes with Windows Mobile.
Internet Explorer Mobile is an Internet browser developed by Microsoft for Pocket PC and Handheld PC that comes loaded by default with Windows Mobile and Windows CE for Handheld PC.
Windows Media Player for Windows Mobile.
Client for PPTP VPNs.
Internet Connection Sharing (ICS) which in mobile phones allows attached computers to share internet connections via USB and Bluetooth.
Coherent file system similar to that of Windows 9/Windows NT and support for many of the same file types.
Ability to multitask.
Symbian is an operating system (OS) designed for mobile devices and smartphones, with associated libraries, user interface, frameworks and reference implementations of common tools, originally developed by Symbian Ltd. It was a descendant of Psion's EPOC and runs exclusively on ARM processors, although an unreleased x86 port existed.
In 2008 the former Symbian Software Limited was acquired by Nokia and a new independent non-profit organization called the Symbian Foundation was established. Symbian OS and its associated user interfaces S60, UIQ and MOAP(S) were contributed by their owners to the foundation with the objective of creating the Symbian platform as a royalty-free, open source software. The resulting Symbian platform has been designated as the successor to Symbian OS, following the official launch of the Symbian Foundation in April 2009. The process of publishing the source code under the Eclipse Public License (EPL) was slated for completion in 2010.
Symbian features pre-emptive multitasking and memory protection, like other operating systems (especially those created for use on desktop computers). EPOC's approach to multitasking was inspired by VMS and is based on asynchronous server-based events.
Symbian OS was created with three systems design principles in mind:
the integrity and security of user data is paramount,
user time must not be wasted, and
all resources are scarce.
To best follow these principles, Symbian uses a microkernel, has a request-and-callback approach to services, and maintains separation between user interface and engine. The OS is optimized for low-power battery-based devices and for ROM-based systems (e.g. features like XIP and Sreentrancy in shared libraries). Applications, and the OS itself, follow an object-oriented design: Model-view-controller (MVC).
Later OS iterations diluted this approach in response to market demands, notably with the introduction of a real-time kernel and a platform security model in versions 8 and 9.
There is a strong emphasis on conserving resources which is exemplified by Symbian-specific programming idioms such as descriptors and a cleanup stack. There are similar techniques for conserving disk space (though the disks on Symbian devices are usually flash memory). Furthermore, all Symbian programming is event-based, and the CPU is switched into a low power mode when applications are not directly dealing with an event. This is achieved through a programming idiom called active objects. Similarly the Symbian approach to threads and processes is driven by reducing overheads.
The Symbian kernel (EKA2) supports sufficiently-fast real-time response to build a single-core phone around it-that is, a phone in which a single processor core executes both the user applications and the signaling stack. This is a feature which is not available in Linux. This has allowed Symbian EKA2 phones to become smaller, cheaper and more power efficient than their predecessors.
Devices that use Symbian OS
On 16 November 2006, the 100 millionth smart phones running the OS was shipped.
The Ericsson R380, in 2000, was the first commercially available phone based on Symbian OS. As with the modern "FOMA" phones, this device was closed, and the user could not install new C++ applications. Unlike those, however, the R380 could not even run Java applications, and for this reason, some have questioned whether it can properly be termed a 'smart phone'.
The UIQ interface was used for PDAs such as Sony Ericsson P800, P900, W950 and the RIZR Z8 and RIZR Z10.
The Nokia S60 interface is used in various phones, the first being the Nokia 7650. The Nokia N-Gage and Nokia N-Gage QD gaming/smart phone combos are also S60 platform devices. It was also used on other manufacturers' phones such as the Siemens SX1 and Samsung SGH-Z600. Recently, more advanced devices using S60 include the Nokia 6xxx, the Nseries (except Nokia N8xx and N9xx), the Eseries and some models of the Nokia XpressMusic mobiles.
The Nokia 9210, 9300 and 9500 Communicator smartphones used the Nokia Series 80 interface.
The Nokia 7710 is the only device currently using the Nokia Series 90 interface.
Fujitsu, Mitsubishi, Sony Ericsson and Sharp developed phones for NTT DoCoMo in Japan, using an interface developed specifically for DoCoMo's FOMA "Freedom of Mobile Access" network brand. This UI platform is called MOAP "Mobile Oriented Applications Platform" and is based on the UI from earlier Fujitsu FOMA models.