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    Mac OS X (with X representing Roman numeral ten) is an operating system for Apple’s Macintosh computers. In addition to many distinct end user functionalities, it supports multiple development technologies including UNIX, Java, the proprietary Cocoa and Carbon runtime environments, and a host of open source, Web, scripting, and database applications. Released in 2001, Mac OS X replaced its predecessor, “Classic” Mac OS version 9, effectively introducing a new nomenclature. The following timeline of updates used the same “Mac OS X” prefix:

    • Cheetah (v10.0) – March 2001
    • Puma (v10.1) – September 2001
    • Jaguar (v10.2) – August 2002
    • Panther (v10.3) – October 2003
    • Tiger (v10.4) – April 2005
    • Leopard (v10.5) – October 2007
    • Snow Leopard (v10.6) – June 2009
    • Lion (v10.7) – July 2011
    • Mountain Lion (v10.8) – July 2012
    • Mavericks (v10.9) – October 2013
    • Yosemite (v10.10) – October 2014
    • El Capitan (v10.11) – September 2015

    With Sierra in 2016, Apple began using an even shorter naming convention, simply “macOS”:

    • Sierra (v10.12) – September 2016
    • High Sierra (v10.13) – September 2017
    • Mojave (v10.14) – September 2018
    • Catalina (v10.15) – October 2019
    • Big Sur (v10.16) – June 2020

    Mac OS X features

    Because the legacy Mac OS was losing its competitive edge and lacked a number of in-demand features offered by Windows, Mac OS X was expected to be a major operating system evolution. In addition to major aesthetic upgrades like the Aqua user interface and the Dock, Apple also used Mac OS X to introduce a number of native applications such as Mail, Address Book, and TextEdit.

    Subsequent releases have largely maintained the original look and feel of Mac OS X Cheetah, with small refinements to streamline the user experience. New features have also become standard since the first OS X launch, including Safari, Spotlight, Quick Look, multi-touch gestures, and iCloud.

    One relatively major change had nothing to do with the technology itself beginning with OS X Mavericks in 2013, Apple released updates to its operating system free of charge for Mac users. This is a distinct shift from the ~$130 price tag associated with the original OS X launch and its subsequent updates, a change that CEO Tim Cook reportedly said more closely aligned with the goals of Apple as a company.