Mac OS X

OS X is Apple Inc.'s current Mac OS line of operating systems. Although, under its original name of Mac OS X, it was officially designated as simply "version 10" of the Mac OS, "version 9" has a completely different codebase as well as dramatic changes in user interface. Mac OS had been Apple's primary operating system since 1984, and the family was backward compatible, so OS X could virtualize Mac OS 9 until version 10.5.

Unlike its predecessor, OS X is a UNIX operating system built on technology that had been developed at NeXT through the second half of the 1980s and up until Apple purchased the company in early 1997. It was first released in 1999 as Mac OS X Server 1.0, with a desktop-oriented version (Mac OS X v10.0) following in March 2001. Since then, six more distinct "client" and "server" editions of Mac OS X were released, thereafter starting with Mac OS X v10.7 Lion, OS X Server is no longer offered as a separate operating system product; instead, the server management tools are available for purchase separately. The most recent and current UNIX certified version OS X 10.10 Yosemite was made available on October 16, 2014.

Mac OS X v10.5 Leopard, when running on Intel processors,^[1] Mac OS X v10.6 Snow Leopard,^[2] OS X v10.8 Mountain Lion,^[3] OS X v10.9 Mavericks,^[4] and OS X v10.10 Yosemite^[5] are all certified UNIX systems, conforming to the Single UNIX Specification.

Releases of OS X prior to 10.9 were named after big cats; the previous version of OS X, 10.8, is named Mountain Lion. At the 2013 Apple Worldwide Developers Conference, Apple indicated that OS X 10.9 Mavericks and future OS X releases would be named after California locations.

(Source: Wikipedia)

Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems.

The original operating system was first introduced in 1984 as being integral to the original Macintosh, and referred to as the "System". Referred to by its major revision starting with "System 6 and "System 7", Apple rebranded version 7.6 as "Mac OS" as part of their Macintosh clone program in 1996. The Macintosh, specifically its system software, is credited with having popularized the early graphical user interface concept.

Macintosh operating systems have been released in two major series. Up to major revision 9, from 1984 to 2000, it is historically known as Classic Mac OS. Major revision 10, from 2001 to present, is branded OS X (originally referred to as Mac OS X).^[2] Major revisions to the Macintosh OS are now issued as point revisions, such that, for example, 10.2 is substantially different from 10.5. Both series share a general interface design, and there has been some overlap with shared application frameworks and virtual machine technology for compatibility; but the two series also have deeply different architectures.

(Source: Wikipedia)