What is Mac OS X

Mac OS X is Apple's operating system for its line of Macintosh computers. Its interface, known as Aqua, is built on a Unix foundation. Although it has much of the look and feel of the former Mac OS, features such as preemptive multitasking, symmetric multiprocessing, multithreading, and protected memory give Mac OS X improved stability and performance. For the current version's system requirements, see Apple's Mac OS X Technical Specs.
Currently four Mac OS X-related products are available:
Mac OS X: This is the version most Macintosh owners should use. It is a consumer operating system designed for use on your personal computer. For more information, see Apple's Mac OS X page and Apple's Developer Connection page for Mac OS X.
Mac OS X Server: This is Apple's server operating system. It is similar to the consumer release of Mac OS X, but also includes a suite of network services, such as a print server, file sharing, QuickTime streaming, NetBoot, and advanced web hosting. For more information, see Apple's Mac OS X Server page and Apple's Developer Connection page for Mac OS X Server.
iPhone OS: Based on Mac OS X, versions of iPhone OS run on the iPhone, the iPod Touch, and the iPad. The iPhone OS was designed for handheld devices, and is much more tightly controlled than other versions of Mac OS X. Despite their shared origins, applications (apps) developed for iPhone OS are not compatible with Mac OS X, and vice versa.
Darwin: Darwin is the Unix-like foundation upon which Mac OS X is based. Its code is open source, and it is available as a stand-alone operating system. Although Darwin will run many Unix applications, including the X Window System, it does not have the Mac OS X interface and thus will not run Mac OS X applications. For more information, see Apple's Developer Connection open source page.

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