OS X



The Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, Mac OS X has been included with all new Macintosh computer systems. It is the successor to Mac OS 9, the final release of the "classic" Mac OS, which had been Apple's primary operating system since 1984.

Mac OS X, whose X is the Roman numeral for 10 and is a prominent part of its brand identity, is a Unix-based graphical operating system, built on technologies developed at NeXT between the second half of the 1980s and Apple's purchase of the company in late 1996. From its sixth release Mac OS X 10.5.0 "Leopard" and onwards, every release of Mac OS X gained UNIX 03 certification while running on Intel processors.

The first version released was Mac OS X Server 1.0 in 1999, and a desktop-oriented version, Mac OS X 10.0.0 "Cheetah" followed on March 24, 2001. Releases of Mac OS X are named after big cats: for example, Mac OS X 10.6.0 is usually referred to by Apple and users as "Snow Leopard". The server edition, Mac OS X Server, is architecturally identical to its desktop counterpart, and includes tools to facilitate management of workgroups of Mac OS X machines, and to provide access to network services. These tools include a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others. It is pre-loaded on Apple's Xserve server hardware, but can be run on almost all of Apple's current selling computer models.

Apple also produces specialized versions of Mac OS X for use on four of its consumer devices: the iOS for the iPhone, iPod Touch, and iPad, as well as an unnamed version for the Apple TV.

History
Mac OS X is based upon the Mach kernel. Certain parts from FreeBSD's and NetBSD's implementation of Unix were incorporated in Nextstep, the core of Mac OS X. Nextstep was the object-oriented operating system developed by Steve Jobs' company NeXT after he left Apple in 1985. While Jobs was away from Apple, Apple tried to create a "next-generation" OS through the Taligent, Copland and Gershwin projects, with little success.

Eventually, NeXT's OS, then called OPENSTEP, was selected to be the basis for Apple's next OS, and Apple purchased NeXT outright. Steve Jobs returned to Apple as interim CEO, and later became CEO, shepherding the transformation of the programmer-friendly OPENSTEP into a system that would be adopted by Apple's primary market of home users and creative professionals. The project was first known as Rhapsody and was later renamed to Mac OS X.

Mac OS X Server 1.x, was incompatible with software designed for the original Mac OS and had no support for Apple's own IEEE 1394 interface (FireWire). Mac OS X 10.x included more backward compatibility and functionality by including the Carbon API as well as FireWire support. As the operating system evolved, it moved away from the legacy Mac OS to an emphasis on new "digital lifestyle" applications such as the iLife suite, enhanced business applications (iWork), and integrated home entertainment (the Front Row media center). Each version also included modifications to the general interface, such as the brushed metal appearance added in version 10.3, the non-pinstriped titlebar appearance in version 10.4, and in 10.5 the removal of the previous brushed metal styles in favor of the "Unified" gradient window style.

Description
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 has released this family of software as a free and open source operating system named Darwin. 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 Openstep, which was designed to be portable, to ease the transition from one platform to another. For example, Nextstep was ported from the original 68k-based NeXT workstations to x86 and other architectures before NeXT was purchased by Apple, and OpenStep was later ported to the PowerPC architecture as part of the Rhapsody project.

The most visible change was the Aqua theme. The use of soft edges, translucent colors, and pinstripes – similar to the hardware design of the first iMacs – brought more texture and color to the user interface when compared to what OS 9 and OS X Server 1.0's "Platinum" appearance had offered. According to John Siracusa, an editor of Ars Technica, the introduction of Aqua and its departure from the then conventional look "hit like a ton of bricks." Bruce Tognazzini (who founded the original Apple Human Interface Group) said that the Aqua interface in Mac OS X 10.0.0 represented a step backwards in usability compared with the original Mac OS interface. Third-party developers started producing skins for customizable applications for Mac and other operating systems which mimicked the Aqua appearance. To some extent, Apple has used the successful transition to this new design as leverage, at various times threatening legal action against people who make or distribute software with an interface the company claims is derived from its copyrighted design.

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.

The Darwin sub-system in Mac OS X is in charge of managing the filesystem, which includes the Unix permissions layer. In 2003 and 2005, two Macworld editors expressed criticism of the permission scheme; Ted Landau called misconfigured permissions "the most common frustration" in Mac OS X, while Rob Griffiths suggested that some users may even have to reset permissions every day, a process which can take up to 15 minutes. More recently, another Macworld editor, Dan Frakes, called the procedure of repairing permissions vastly overused. He argues that Mac OS X typically handles permissions properly without user interference, and resetting permissions should just be tried when problems emerge.

As of 2009, Mac OS X is the second most popular general-purpose operating system in use for the internet, after Microsoft Windows, with a 4.5% market share according to statistics compiled by Net Applications. In contrast, it is the most successful UNIX-like desktop operating system on the internet, estimated at over 4 times the penetration of the free Linux. Eighteen languages are available for the "base" language (that which is used for sub-user environments, such as the user login screen) at the first screen of the installation DVD. All of the eighteen user languages for the system menus, messages, and other functions are installed by default and can be chosen from the System Preferences. As of OS 10.6, the languages are English, Japanese, French, German, Spanish, Italian, Dutch, Swedish, Danish, Norwegian, Finnish, Traditional Chinese, Simplified Chinese, Korean, Brazilian Portuguese, European Portuguese, Russian, and Polish. Input methods for typing in dozens of scripts can be chosen independently of the system language.

Software
The APIs that Mac OS X inherited from OpenStep are not backward compatible with earlier versions of Mac OS. These APIs were created as the result of a 1993 collaboration between NeXT Computer and Sun Microsystems and are now referred to by Apple as Cocoa. This heritage is highly visible for Cocoa developers, since the "NS" prefix is ubiquitous in the framework, standing variously for Nextstep or NeXT/Sun. The official OpenStep API, published in September 1994, was the first to split the API between Foundation and Application Kit and the first to use the "NS" prefix. Apple's Rhapsody project would have required all new development to use these APIs, causing much outcry among existing Mac developers. All Mac software that did not receive a complete rewrite to the new framework would run in the equivalent of the Classic environment. To permit a smooth transition from Mac OS 9 to Mac OS X, the Carbon Application Programming Interface (API) was created. Applications written with Carbon can be executed natively on both systems. Carbon was not included in the first product sold as Mac OS X, Mac OS X Server (now known as Mac OS X Server 1.x).

Mac OS X also used to support the Java Platform as a "preferred software package" – in practice this means that applications written in Java fit as neatly into the operating system as possible while still being cross-platform compatible, and that graphical user interfaces written in Swing look almost exactly like native Cocoa interfaces. Traditionally, Cocoa programs have been mostly written in Objective-C, with Java as an alternative. However, on July 11, 2005, Apple announced that "features added to Cocoa in Mac OS X versions later than 10.4 will not be added to the Cocoa-Java programming interface."

Since Mac OS X is POSIX compliant, many software packages written for the * BSDs or Linux can be recompiled to run on it. Projects such as Fink, MacPorts and pkgsrc provide pre-compiled or pre-formatted packages. Since version 10.3, Mac OS X has included X11.app, Apple's version of the X Window System graphical interface for Unix applications, as an optional component during installation. Up to and including Mac OS X 10.4.0 (Tiger), Apple's implementation was based on the X11 Licensed XFree86 4.3 and X11R6.6. All bundled versions of X11 feature a window manager which is similar to the Mac OS X look-and-feel and has fairly good integration with Mac OS X, also using the native Quartz rendering system. Earlier versions of Mac OS X (in which X11 has not been bundled) can also run X11 applications using XDarwin. With the introduction of version 10.5 Apple switched to the X.org variant of X11.

Hardware
For the early releases of Mac OS X, the standard hardware platform supported was the full line of Macintosh computers (laptop, desktop, or server) based on PowerPC G3, G4, and G5 processors. Later versions discontinued support for some older hardware; for example, Panther does not support "beige" G3s, and Tiger does not support systems that pre-date Apple's introduction of integrated FireWire ports (the ports themselves are not a functional requirement). Mac OS X 10.5.0 "Leopard", introduced October 2007, has dropped support for all PowerPC G3 processors and for PowerPC G4 processors with clock rates below 867 MHz. Mac OS X 10.6.0 "Snow Leopard" supports Macs with Intel processors, not PowerPC.

Tools such as XPostFacto and patches applied to the installation disc have been developed by third parties to enable installation of newer versions of Mac OS X on systems not officially supported by Apple. This includes a number of pre-G3 Power Macintosh systems that can be made to run up to and including Mac OS X 10.2 Jaguar, all G3-based Macs which can run up to and including Tiger, and sub-867 MHz G4 Macs can run Leopard by removing the restriction from the installation DVD or entering a command in the Mac's Open Firmware interface to tell the Leopard Installer that it has a clock rate of 867 MHz or greater. Except for features requiring specific hardware (e.g. graphics acceleration, DVD writing), the operating system offers the same functionality on all supported hardware.

PowerPC versions of Mac OS X prior to Leopard retain compatibility with older Mac OS applications by providing an emulation environment called Classic, which allows users to run Mac OS 9 as a process within Mac OS X, so that most older applications run as they would under the older operating system. Classic is not supported on Intel-based Macs or in Mac OS X 10.5.0 "Leopard", but users still requiring Classic applications on Intel Macs can use the SheepShaver emulator to run Mac OS 9 on top of Leopard.

Apple–Intel transition
In April 2002, eWeek announced a rumor that Apple had a version of Mac OS X code-named Marklar which ran on Intel x86 processors. The idea behind Marklar was to keep Mac OS X running on an alternative platform should Apple become dissatisfied with the progress of the PowerPC platform. These rumors subsided until late in May 2005, when various media outlets, such as the Wall Street Journal and CNET, announced that Apple would unveil Marklar in the coming months.

On June 6, 2005, Steve Jobs confirmed these rumors when he announced in his keynote address at the annual Apple Worldwide Developers Conference that Apple would be making the transition from PowerPC to Intel processors over the following two years, and that Mac OS X would support both platforms during the transition. Jobs also confirmed rumors that Apple had versions of Mac OS X running on Intel processors for most of its developmental life. The last time that Apple switched CPU families—from the Motorola 68K CPU to the IBM/Motorola PowerPC—Apple included a Motorola 68K emulator in the new OS that made almost all 68K software work automatically on the new hardware. Apple had supported the 68K emulator for 11 years, but stopped supporting it during the transition to Intel CPUs. Included in the new OS for the Intel-based Macs is Rosetta, a binary translation layer which enables software compiled for PowerPC Mac OS X to run on Intel Mac OS X machines. Apple dropped support for Classic mode on the new Intel Macs. Third party emulation software such as Mini vMac, Basilisk II and SheepShaver provides support for some early versions of Mac OS. A new version of Xcode and the underlying command-line compilers support building universal binaries that will run on either architecture.

PowerPC-only software is supported with Rosetta, though applications may have to be rewritten to run properly on the newer OS X for Intel. Apple initially encouraged developers to produce universal binaries with support for both PowerPC and x86. There is a performance penalty when PowerPC binaries run on Intel Macs through Rosetta. Moreover, some PowerPC software, such as kernel extensions and System Preferences plugins, are not supported on Intel Macs. Some PowerPC applications would not run on Intel OS X at all. Plugins for Safari need to be compiled for the same platform as Safari, so when Safari is running on Intel it requires plug-ins that have been compiled as Intel-only or universal binaries, so PowerPC-only plug-ins will not work. While Intel Macs are able to run PowerPC, x86, and universal binaries, PowerPC Macs support only universal and PowerPC builds.

Support for the PowerPC platform was dropped after Mac OS X 10.5.0. Such cross-platform capability already existed in Mac OS X's lineage; Openstep was ported to many architectures, including x86, and Darwin included support for both PowerPC and x86. Apple stated that Mac OS X would not run on Intel-based personal computers aside from its own, but a hacked version of the OS compatible with conventional x86 hardware was developed by the OSx86 community.

On June 8, 2009, Apple announced at its Worldwide Developers Conference that Snow Leopard (version 10.6.0) would drop support for PowerPC processors and be Intel-only. However, Rosetta is still supported. In Snow Leopard, Rosetta is not installed by default, but it is available on the installation DVD as an installable add-on and is installed automatically via the Internet when first attempting to run a PowerPC-based application.

Features
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, graphic, or widget is drawn on-screen using 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 10.2.0, 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 10.3.0, 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, FileVault 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 10.5.0, all system icons are scalable up to 512×512 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 10.5.0 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.

Versions
With the exception of Mac OS X Server 1.0 and the original public beta, Mac OS X versions were named after big cats until the release of OS X 10.9 (Mavericks) that was named after a surfing beach in California. Prior to its release, version 10.0 was code named "Cheetah" internally at Apple, and version 10.1 was code named internally as "Puma". After the immense buzz surrounding version 10.2, codenamed "Jaguar", Apple's product marketing began openly using the code names to promote the operating system. 10.3.0 was marketed as "Panther", 10.4 as "Tiger", and 10.5 as "Leopard". "Snow Leopard" is the name for the current release, version 10.6. "Panther", "Tiger", "Leopard", "Snow Leopard", "Lion" and "Mountain Lion" are registered as trademarks of Apple, but "Cheetah", "Puma" and "Jaguar" have never been registered. Apple has also registered "Lynx" and "Cougar" as trademarks, though these were allowed to lapse. Computer retailer Tiger Direct sued Apple for its use of the name "Tiger". On May 16, 2005 a US federal court in the Southern District of Florida ruled that Apple's use does not infringe on Tiger Direct's trademark.

Public Beta: "Kodiak"
Apple released to the public, on September 13, 2000, a "preview" version of Mac OS X (internally codenamed Kodiak) in order to gain feedback from users, which cost $29.95. The "PB" as it was known marked the first public availability of the Aqua interface and Apple made many changes to the UI based on customer feedback. Mac OS X Public Beta expired and ceased to function in Spring 2001.

Version 10.0: "Cheetah"
On March 24, 2001, Apple released Mac OS X 10.0.0 (internally codenamed Cheetah). The initial version was slow, incomplete, and had very few applications available at the time of its launch, mostly from independent developers. While many critics suggested that the operating system was not ready for mainstream adoption, they recognized the importance of its initial launch as a base on which to improve. Simply releasing Mac OS X was viewed by the Macintosh community as a great accomplishment, for attempts to completely overhaul the Mac OS had been underway since 1996, and delayed by countless setbacks. Following some bug fixes, kernel panics became much less frequent.

Version 10.1: "Puma"
Later that year on September 25, 2001, Mac OS X 10.1.0 (internally codenamed Puma) was released. It had better performance and provided missing features, such as DVD playback. Apple released 10.1 as a free upgrade CD for 10.0 users, in addition to the US$129 boxed version for people running Mac OS 9. It was discovered that the upgrade CDs were full install CDs that could be used with Mac OS 9 systems by removing a specific file; Apple later re-released the CDs in an actual stripped-down format that did not facilitate installation on such systems. On January 7, 2002, Apple announced that Mac OS X was to be the default operating system for all Macintosh products by the end of that month.

Version 10.2: "Jaguar"
On August 23, 2002, Apple followed up with Mac OS X 10.2.0 "Jaguar", the first release to use its code name as part of the branding. It brought great performance enhancements, a sleeker look, and many powerful enhancements (over 150, according to Apple ), including Quartz Extreme for compositing graphics directly on an ATI Radeon or Nvidia GeForce2 MX AGP-based video card with at least 16 MB of VRAM, a system-wide repository for contact information in the new Address Book, and an instant messaging client named iChat. The Happy Mac which had appeared during the Mac OS startup sequence for almost 18 years was replaced with a large grey Apple logo with the introduction of Mac OS X v10.2.

Version 10.3: "Panther"
Mac OS X 10.3.0 "Panther" was released on October 24, 2003. In addition to providing much improved performance, it also incorporated the most extensive update yet to the user interface. Panther included as many or more new features as Jaguar had the year before, including an updated Finder, incorporating a brushed-metal interface, Fast user switching, Exposé (Window manager), FileVault, Safari, iChat AV (which added videoconferencing features to iChat), improved Portable Document Format (PDF) rendering and much greater Microsoft Windows interoperability. Support for some early G3 computers such as "beige" Power Macs and "WallStreet" PowerBooks was discontinued.

Version 10.4: "Tiger"
Mac OS X 10.4.0 "Tiger" was released on April 29, 2005. Apple stated that Tiger contained more than 150+ new features. As with Panther, certain older machines were no longer supported; Tiger requires a Mac with a built-in FireWire port. Among the new features, Tiger introduced Spotlight, Dashboard, Smart Folders, updated Mail program with Smart Mailboxes, QuickTime 7, Safari 2, Automator, VoiceOver, Core Image and Core Video. The initial release of the Apple TV used a modified version of Tiger with a different graphical interface and fewer applications and services. On January 10, 2006, Apple released the first Intel-based Macs along with the 10.4.4 update to Tiger. This operating system functioned identically on the PowerPC-based Macs and the new Intel-based machines, with the exception of the Intel release dropping support for the Classic environment. Only PowerPC Macs can be booted from retail copies of the Tiger client DVD, but there is a Universal DVD of Tiger Server 10.4.7 (8K1079) that can boot both PowerPC and Intel Macs.

Version 10.5: "Leopard"
Mac OS X 10.5.0 "Leopard" was released on October 26, 2007. It was called by Apple "the largest update of Mac OS X". It brought more than 300 new features. Leopard supports both PowerPC- and Intel x86-based Macintosh computers; support for the G3 processor was dropped and the G4 processor required a minimum clock rate of 867 MHz, and at least 512 MB of RAM to be installed. The single DVD works for all supported Macs (including 64-bit machines). New features include a new 3D dock, an updated Finder, Time Machine, Spaces, Boot Camp pre-installed, full support for 64-bit applications (including graphical applications), new features in Mail and iChat, and a number of new security features. Leopard is an Open Brand UNIX 03 registered product on the Intel platform. It was also the first BSD-based OS to receive UNIX 03 certification. Leopard dropped support for the Classic Environment and all Classic applications. It was the final version of Mac OS X to support the PowerPC architecture.

Version 10.6: "Snow Leopard"
Mac OS X 10.6.0 "Snow Leopard" was released on August 28, 2009. Rather than delivering big changes to the appearance and end user functionality like the previous releases of Mac OS X, Snow Leopard focuses on "under the hood" changes, increasing the performance, efficiency, and stability of the operating system. For most users, the most noticeable changes are: the disk space that the operating system frees up after a clean install compared to Mac OS X 10.5 Leopard, a more responsive Finder rewritten in Cocoa, faster Time Machine backups, more reliable and user friendly disk ejects, a more powerful version of the Preview application, as well as a faster Safari web browser.

The rewrite of Finder in Apple's native Cocoa API allows the Finder to take advantage of the integrated 64-bit technology, as well as Grand Central Dispatch, use a more user-friendly disk-eject (clearer dialogs will notify the user of what services or programs are using a given disk), and provides it a more responsive overall feel.

The new Safari 4 includes a boost in JavaScript and HTML performance, which results in faster web browsing. The majority of this performance boost is enabled by the new SquirrelFish JavaScript interpreter, improving the JavaScript rendering performance of Safari by over 50%. The new Top Sites also displays the most frequently visited and/or bookmarked sites in a panorama view, allowing the user to easily access their favorite sites along with a new Cover Flow view for the user's browsing history. Safari 4 is now also more crash resistant, being able to isolate plug-ins which are the number one cause of web browser crashes.

Mac OS X v10.6 also features Microsoft Exchange Server support for Mail, iCal, and Address Book, new 64-bit technology capable of supporting greater amounts of RAM, an all new QuickTime X with a refreshed user interface and more functionality that used to be only available to QuickTime Pro owners.

Back-end platform changes include improved support for multi-core processors through Grand Central Dispatch which attempts to ease the development of applications with multi-core support, and thus improve their CPU utilization. It used to be that developers needed to code their programs in such a way that their software would explicitly take advantage of the multiple cores, which could easily become a tedious and troublesome task, especially in complex software. It also includes advanced GPU performance with OpenCL (a cross platform open standard for GPGPU distinct from CUDA, Dx11 Compute Shader or STREAM) by providing support to offload work normally only destined for a CPU to the graphic card's GPU. This can be especially useful in tasks that can be heavily parallelized.

Snow Leopard only supports machines with Intel CPUs, requires at least 1 GB of RAM, and drops default support for applications built for the PowerPC architecture (Rosetta can be installed as an additional component to retain support for PowerPC-only applications).

Release and distribution
On June 6, 2011, at the Apple Worldwide Developers Conference, it was announced that the official release for Lion would be in July 2011. The specific release date of July 20 was not confirmed until the day before by Apple CFO, Peter Oppenheimer, as part of Apple's 2011 third-quarter earnings announcement.[10]

Apple did not initially announce any physical media distribution for Lion, such as a set of CD-ROMs or a DVD-ROM as used for prior releases. Instead, the operating system was available exclusively as a download from the Mac App Store for US$29.99.[11][12] The only prior version of OS X that supported the Mac App Store was Snow Leopard, which implied that any machines that support Lion currently running Tiger or Leopard would first have to be upgraded to Snow Leopard, as opposed to permitting a direct upgrade to Lion.

Apple later announced two alternative distribution mechanisms for the benefit of users without broadband Internet access: in-store downloads at retail Apple Stores, and a USB flash drive containing the OS, priced at US$69, available through the online Apple Store beginning in August.[13] The USB distribution supported a direct upgrade to Lion from OS X versions prior to Snow Leopard, and allowed for a "clean install" of 10.7. On August 4 2011, Apple started to take orders for Mac OS X Lion's USB installation flash drives for $69.99.[14] The Server portion of Lion is available as a separate download from the Mac App Store for US$49.99, which is in addition to the purchase price of Lion itself.[15]

Hardware support
The first Developer Preview of Lion added TRIM support for SSD drives shipped with Macs; support is also included in the final version of Snow Leopard (10.6.8) shipping with MacBook Pros before July 20, 2011. There was no official TRIM support added to 10.6 or 10.7 for non-Apple SSDs.[16]

System requirements

 * x86-64 CPU (Macs with an Intel Core 2 Duo, Intel Core i3, Intel Core i5, Intel Core i7, or Xeon processor.)[11][17]
 * At least 2GB of RAM[18]
 * Mac OS X 10.6.6 or later (Mac OS X 10.6.8 is recommended)[18]
 * At least 7 GB of free hard drive space[18]


 * AirDrop is supported on the following Mac models:


 * [18] MacBook Pro (late 2008 or newer),


 * MacBook Air (late 2010 or newer),
 * MacBook (late 2008 or newer),
 * iMac (early 2009 or newer),
 * Mac mini (mid 2010 or newer),


 * Mac Pro (early 2009 with AirPort Extreme card and mid 2010 or newer).

New or changed features
Some new features were announced at the "Back to the Mac" keynote in October 2010, and the Apple website was updated in February 2011 with more details.

Other features were announced at the WWDC 2011 keynote or on Apple's Mac OS X Lion Web site after the keynote. Apple states that there are over 250 new or changed features in Lion, including:


 * Address Book now uses an iPad-like user interface. It also includes improved Yahoo support and FaceTime calling.[19]

AirDrop – Lion-to-Lion direct file sharing via Wi-Fi Direct. No wireless access point required.[20]


 * Address space layout randomization – Address space layout randomization (ASLR), a security technique that puts important data in unpredictable locations, making it harder to target known weaknesses, is available for 32-bit applications, and "has been improved for all applications", in Lion.[21]


 * Apple Push Notification Service – Send over-the-air alerts, such as news updates or social networking status changes, using Apple's Push Notification service to applications that support APNS. APNS allows Mac OS X Lion and iOS clients to receive push changes to items such as mail, calendar and contacts from a configured OS X Lion Server.[22]

Auto Save – As in iOS, documents in applications written to use Auto Save will be saved automatically so users don't have to worry about manually managing their documents.[24]
 * Auto-correction now behaves much like on iOS devices, displaying an iOS-like popup box.[23]


 * Emoji support – Apple has added a new Emoji font commonly used in chat to express ideograms.[23][25]


 * Exposé in the Dock, a way of activating Exposé for a single application from the Dock, a feature added in Mac OS X 10.6,[26] is altered. One must now double-tap with two fingers on a dock icon to initiate single application exposé, or simply right-click or control-click and select Show All Windows.


 * FaceTime comes bundled with Lion.[12]


 * FileVault now offers full disk encryption and added security with XTS-AES 128 data encryption. Support for FileVault on external hard drives has also been added.[27]


 * Finder improvements – Finder search allows multiple search criteria to be specified without creating a smart folder, Finder search offers suggestions, files can be grouped by various attributes, and one can now merge files under two folders with the same name – a prompt will appear asking whether one wants to replace or keep both files.[28][29]


 * The navigation sidebar lost the ability to show the specific icon of a map[vague] or volume (by default; there is a hack to still add the old ability), instead it shows a grey standard map icon.


 * Font Book 3—Font Book 3 now provides more flexible displays of character glyphs supplied by a particular font face. Duplicate font files are now flagged with a warning icon, and can be fixed automatically or resolved manually.[25]


 * Full-screen apps – Native, system-wide support for full-screen applications running in their own space. Supporting applications display a new button at the top right of application window, this button opens applications in full-screen mode.[30]


 * High-quality multilingual speech voices – users can download new high-quality voices in more than forty languages and dialects.[31][32]


 * iCal has an updated user interface, an annual view, and support for a full-screen view.[33][34]

iChat now has support for logging into Yahoo! Messenger. Users can audio- and video-chat with other iChat users using their Yahoo! accounts.[35][36]


 * Languages/Localization – Arabic, Czech, Turkish and Hungarian are added as full system languages, to make the total number of twenty-two languages available in Mac OS X.[37]


 * Launchpad – An application launcher that displays an iOS-like icon grid of installed applications. It features the ability to make multiple pages and group apps into folders that function the same as folders in iOS.[38]


 * Mac App Store – An application store built in the image of the iOS App Store. Like in iOS, it will provide ways for shoppers to discover apps, one-click installation of apps, and one-click updates of all or selected installed applications.[4][39][40] Despite being announced as a future feature of Lion, the Mac App Store was released for Mac OS X Snow Leopard on January 6, 2011 as it was bundled with the Mac OS X 10.6.6 update.[41]


 * Mail 5 – Uses an iPad-like user interface, has a fullscreen-optimized view, uses chronological "Conversations" to organize messages,[42] and supports Exchange 2010 (but not through the Exchange ActiveSync protocol, as iOS).[43]


 * Mission Control replaces the "All windows" Exposé feature. It gives an overview of all running applications just like "All windows" but groups windows from the same application. At the top of the screen it gives quick access to the Dashboard, Spaces, and running full screen applications.[4][44]


 * Multi-touch gestures – Similar to iOS, additional gestures performed using a multi-touch input device (e.g. Magic Mouse, Magic Trackpad) will allow the user to scroll, swipe to different pages, and enter Mission Control.[45] While this is not the first official multi-touch support for Mac OS X, it has been expanded; other frameworks, such as Lux,[46] have already created multi-touch support.


 * Multi-User Screen Sharing—The built-in Screen Sharing feature now allows remote users to log into a separate user account from the one that is currently logged in. That means that while one user is logged into a machine, a second user can login to the same machine remotely, seeing their own desktop and user environment.[47][48]


 * Preview gains several features, including full-screen support and the ability to sign a document just by holding a signed piece of paper up to the camera.[49][50]


 * QuickTime re-incorporates some features from QuickTime Pro. New features cited include Copy/Paste, Insert Clip, Crop Video, Rotate Video, Resize, Trim, and more Export options.[50]


 * Recovery Partition – Apple has introduced a recovery partition that includes utilities generally found on the OS X discs. This partition will allow the user to restore their computer to its original factory state. It also allows for a new copy of OS X Lion to be installed over the internet.[51][52]


 * Resume – Applications resume in the same state when re-opened as already seen in iOS.[53]


 * Safari – With full-screen mode and the new WebKit2 layout engine.[54][55]

Terminal has extra features, including full screen mode.
 * System Information – This feature is a re-design of System Profiler, which has been completely altered with new views which display graphical information on displays, storage devices, memory usage along with other hardware information. The previous layout remains available by clicking "System Report". Early builds of Lion also used System Information as a replacement for "About This Mac",[56] although the final release reinstated the version of this dialog box found in Snow Leopard.


 * TextEdit gains a new graphical toolbar with font selection and text highlighting. The new TextEdit also supports Apple's new automatic file saving and versions technologies.[57][58]


 * Versions – Time Machine-like saving and browsing of past versions of documents for applications written to use Versions.[24]

The complete list from Apple can be found on Apple's website.[59]
 * Vertical text – Lion supports vertical layouts for East Asian languages.[23][58]

Server features
Main article: Mac OS X Server Wiki


 * Server 3 – Making it easier to collaborate, share, and exchange information. Users can quickly switch between a server's home page, My Page, Updates, Wikis, People, and Podcasts. File sharing is simpler, and a new Page Editor is added for easy customization.[15]


 * WebDAV File Sharing – Lion Server delivers wireless file sharing for clients that support WebDAV. Enabling WebDAV in Lion Server gives iOS users the ability to access, copy, and share documents on the server from applications such as Keynote, Numbers, and Pages.[15]

Profile Manager – Profile Manager delivers simple, profile-based setup and management for Mac OS X Lion, iPhone, iPad, and iPod touch devices. It also integrates with existing directory services and delivers automatic over-the-air profile updates using the Apple Push Notification service.[15][60]

User interface changes

 * Redesigned Aqua user interface elements, including buttons and progress bars. The red, yellow and green buttons in the window decorations have also been made smaller.[61]

The metal finish has also been slightly altered. It is now a lighter shade of grey than before and features a speckled texture.[citation needed]
 * Flexible window resizing from any corner or edge of the window,[62][63] similar to window resizing in Microsoft Windows and many window managers for X11.

Scrolling is reversed by default, to act more like a touch screen computer, so that content moves in the direction of finger movement on touch-pad or mouse (with the scrollbar moving in the opposite direction), rather than the scrollbar moving in the direction of finger movement (with the content moving in the opposite direction). Also, like in iOS, scrolling "bounces" when the scroll bar hits the top or bottom of the window.[64]
 * On demand scroll bars now disappear by default when they are not being used, similar to iOS.[62]


 * When resizing a window by clicking on the green button (left-top), a transform-effect animates the enlargement.[citation needed]


 * New windows fly to the front (like opening an app in iOS).[65]


 * The dashboard is now its own space in Mission Control, rather than in previous versions of OS X where the widgets simply flew in and the background dimmed. The "ripple effect" that was seen previously when adding widgets is no longer there due to this change. Users have the option to return to the old dashboard configuration in System Preferences.


 * Tabs, when selected, now appear as being pushed in and darkened as opposed to previous versions where selected tabs were highlighted in aqua blue.[66]

Dropped features

 * Save As[67] – replaced by Duplicate and Revert functions due to the introduction of Auto Save and Versions (only applies to applications modified to support Auto Save, such as TextEdit; applications not modified to support Auto Save, such as Microsoft Word, retain this functionality).


 * Front Row,[68] a media center application. The application has been copied into Lion by third-party users, however its incompatibility with iTunes 10.4 renders some features useless.[69]

Rosetta, software which makes possible the execution of PowerPC software on x86 hardware, is no longer available.[68] This disables some programs that ran on previous versions of Mac OS X.[70] Programs requiring Rosetta to operate are not allowed to be distributed via the Mac App Store.[71]


 * Adobe Flash Player and Apple's Java Runtime Environment (JRE) are not included in new installations of Lion, but both can still be downloaded and installed manually.[68][72][73] Apple will no longer be actively maintaining its JRE, but Software Update will offer to download Snow Leopard's JRE if a user tries to run a Java program without there being a JRE installed.[74] Programs using Java are not allowed to be distributed via the Mac App Store.[71]

iSync, software used for syncing contacts and calendars to third-party mobile phones, is no longer included; however, iSync v3.1.2 from Snow Leopard continues to work.[citation needed]


 * Remote Install Mac OS X, software which allows OS X to be installed using the Remote Disk feature. Using Target Disk Mode, users can circumvent this omission.[75] This is replaced by the Recovery Partition, which does the exact same thing but without needing an external disk.

Apple USB Modem is not compatible with Lion.[76]

Reception
Reception for OS X Lion has generally been positive, but tempered by a substantial backlash by "Pro" users with workflows affected by the Autosave/Revert workflow.[77]


 * In an extensive review of the operating system, Ars Technica recommended Lion.[61] They noted that it feels like it is the start of a new line of operating systems that will continue to be influenced by Apple's iOS platform.[61] The review also compared the introduction of Lion, along with its new conventions that change traditional ways of computing, to the original Mac OS X and when it replaced the classic Mac OS.[61]


 * Macworld called Lion a "radical revision", praising the changes made to the operating system to be more user friendly to new Mac users that are familiar with the iOS interface, while criticizing the limited utility of the interface. Ultimately, the magazine considered Lion an operating system worth getting, giving it 4.5 out of 5 stars.[78]


 * guardian.co.uk called Lion a substantial improvement from its predecessors, and considered it a "steal" given its price.[79]

On the other hand, Gizmodo stated that the new interface "feels like a failure" and concluded by saying that "it doesn't feel like a must-have upgrade".[80]


 * Ted Landau of MacObserver also had serious criticism of Lion, reversing his earlier praise of Autosave and writing "Auto Save takes irritatingly long when working with large documents. Still others lament the loss of the Save As… command, noting that the new Duplicate option is not as convenient to use.


 * The consensus is that none of this would matter much — if you could disable Auto Save. If you like how it works, leave things as is. Otherwise, get rid of it. But Lion offers no way to turn Auto Save off. This is the heart of the “my way or the highway” complaint. A posting sums it up: “The new features are intrusive, non-respectful of the users’ choices, and cannot be changed.”[77]


 * Due to Lion's enhanced security features, including application sandboxing, Dino Dai Zovi, principal of security consultancy Trail of Bits and the coauthor (with Charles Miller) of The Mac Hacker's Handbook, characterized Lion's security as "a significant improvement, and the best way that I've described the level of security in Lion is that it's Windows 7, plus, plus. I generally tell Mac users that if they care about security, they should upgrade to Lion sooner rather than later, and the same goes for Windows users, too."[81]

Software incompatibilities
Applications depending on Rosetta, such as Office for Mac 2004[82] and Quicken for Mac 2007,[83] are no longer supported. This affects applications listed as Classic or PowerPC in System Profiler. Unix package managers for Mac OS X such as Fink[84] and MacPorts[85] require reinstalling and then running Xcode.

Version 10.8: "Mountain Lion"
Mac OS X 10.8.0 "Mountain Lion" was released on July 25, 2012. It still has the Mac App store along with plenty of other features from iOS 5 and iOS 6. Some of these are iMessage, Reminders, Notification Center, Notes and Share Sheets.

OS X Mountain Lion was officially announced by Apple Inc. on their website on February 16 as a successor to Mac OS X 10.7 "Lion". As of 6 March 2012, it was still in development and it is available for download exclusively to Apple Developers with a paid membership for free as a beta version. [edit]System requirements

As of Developer Preview 1, Mountain Lion supports most of the same hardware as Lion: x86-64 CPU (Macs with an Intel Core 2 Duo, i3, i5, i7, or Xeon processor)[4] An EFI64-based system (iMac (Late 2007 or newer), Mac mini (Early 2009 or newer), Mac Pro (Early 2008 or newer), MacBook (Late 2008 or newer), Xserve (Early 2009 or newer), MacBook Pro (Mid 2007 or newer), MacBook Air (Late 2008 or newer)) At least 8 GB of free hard drive space[5] OS X Mountain Lion no longer supports ATI's Mobility Radeon X1600 or Radeon X1900, Intel's GMA 950 or GMA X3100, or NVIDIA's GeForce 7300 graphics processors.[6] [edit]New or changed features

Deeper integration of iCloud, which includes new Open and Save dialog boxes across built-in applications, iWork and third-party applications via an API. Applications that make use of this API support a new user interface to view and manage documents in the cloud that are specific to the application being used.[7] Automatic synchronization of documents in iWork with iCloud Messages – a multi-protocol instant messaging and texting client (replacing iChat); supports the iMessage service. Also avaialble on Mac OS X 10.7 "Lion") as a beta version.[8] Reminders – a to-do list application, also on iOS, separated from Calendar[9] Notes – previously in iOS and separated from Mail into its own application, with support for desktop notes added[10] Share Sheets – a "Share" button and dialog box in Safari and other applications[11] Game Center – borrowed from iOS[12] AirPlay Mirroring – remote broadcast of OS X desktop to Apple TV via AirPlay[13] Gatekeeper[14] – an anti-malware feature based on digital signatures and the Mac App Store Twitter integration[15]

Notification Center in OS X Mountain Lion. Notification Center – A desktop version similar to the one introduced in iOS 5. Application pop-ups are now concentrated on the corner of the screen, and the Center itself is pulled from the right side of the screen.[16] More Chinese features – has additional features for users in China, including support for Baidu as an option for Safari search engine, QQ, 163.com and 126.com services for Mail, Contacts and Calendar, Youku, Tudou and Sina Weibo are integrated into share sheets.[17] Time Machine is able to do rotating backups on more than one storage medium.[18] [edit]Renamed applications iCal is renamed "Calendar"[7] Address Book is renamed "Contacts"[7] iChat has been enhanced and renamed "Messages"[8] (see above) [edit]Dropped features RSS support in Mail and Safari has been removed[19] Software Update – has been unified into the Mac App Store[20] X11.app – users are directed to the open source XQuartz project instead[21] [edit]