Darwin (operating system)

Darwin is a free Unix operating system made by the Apple company and the basis for Apple's proprietary operating systems that evolved from Mac OS X: macOS for Mac-branded personal computers, iOS for the iPod and iPhone mobile devices, iPadOS for the iPad, tvOS for the Apple TV set-top box, and watchOS for the Apple Watch. It was first made available as Darwin 0.1 on March 16, 1999, along with Mac OS X Server 1.0.

In January 1997, NeXT was taken over by Apple and with it the operating system OPENSTEP, still called NeXTStep until version 3, which had just been released in version 4.0. This was extended under the name Rhapsody by, among other things, the Macintosh interface in Platinum design, as it was also used in Mac OS 8, as well as the virtualization environment Blue Box, under which Mac OS 8.1 could be run virtualized. NeXTStep, OPENSTEP and Rhapsody use large parts of BSD Unix as a basis for an operating system running on multiple platforms and computer architectures - Rhapsody should have run on multiple platforms as well, but Apple stopped the release of the completed Rhapsody for PowerPC Macintosh and x86 PC systems in 1998, as a multi-platform strategy had been recognized as failing in the market. At WWDC 1998, Apple announced the merger of Mac OS (then currently in version 8, until 1997 still System 7) with Rhapsody, which was to be named "Mac OS X". According to Steve Jobs, Mac OS X was supposed to be released in 1999. However, since it was not yet ready in 1999, Rhapsody was released as a pure Macintosh server operating system under the name "Mac OS X Server 1.0" - as well as its open source BSD core as Darwin 0.1.

On this basis - Rhapsody and Darwin as its open source part - the development of Mac OS X 10.0 was started and with the releases of the Developer Previews and the Public Beta, some versions of Darwin were also released starting in 1999 which could be installed on a Macintosh computer running Mac OS. However, after the finished version of Mac OS X 10.0 "Cheetah" in 2001, Apple lost interest in an official Darwin distribution and since then only provides the source code for Darwin, which forms the basis of the respective version of the proprietary operating system. The further development of Darwin in this form is closely interwoven with the development of Apple operating systems.

Since integral parts of macOS and iOS are not open source, Darwin lacks the graphical user interface Aqua as well as Quartz, OpenGL, QuickTime and the programming interfaces Cocoa and Carbon, which is why programs for Mac OS X/OS X/macOS are not executable. Therefore, the few available Darwin distributions use free (FreeBSD-compatible) desktop environments, and e. g. by means of MacPorts a large number of free software can also be used on Darwin without much effort.

Architecture, functional description and system requirements

The source code base of Darwin goes back to 4.4BSD-Lite, which was ‑cleaned of the last remaining original SystemV source lines after the dispute over rights to the UNIX code that ended in 1994.‑ It is available under a free license, the APSL. At the same time, Darwin is a descendant of the NeXT-developed operating system NeXTStep, which was renamed OPENSTEP in 1996 and was still based on 4.3BSD. Apple bought NeXT towards the end of 1996 and further developed the purchased system into Rhapsody. The BSD base system was ported from 4.3BSD to 4.4BSD Lite source code and the kernel from Mach 2.5 to Mach 3. With the release of Mac OS X Developer Preview 1, this kernel was first known as XNU and released as part of the Darwin source code. However, Mach 3 is not fully implemented, but supplemented by parts of the FreeBSD kernel to a hybrid kernel, so that it combines the advantages of a monolithic kernel with the advantages of a microkernel. Parts of the Mach implementation from MkLinux, in which Apple was also involved, were reused.

Darwin runs in different versions on PowerPC processors, x86 processors and on ARM processors. While all applications for Darwin also run on Mac OS X, applications tailored for Mac OS X/OS X/macOS do not necessarily work on Darwin. The mobile operating systems iOS for the iPhone, iPadOS for the iPad, tvOS for the Apple TV, and watchOS for the Apple Watch are also based on Darwin, but the user does not have access to the file system or the command line. This restriction can be lifted in some cases by a jailbreak.

Licensing and marketing

Darwin is published under the Apple Public Source License in source code, which is recognized as a free software license by the Free Software Foundation as of version 2.0. The mascot of Darwin is Hexley, the platypus.

Darwin is the open source core of Apple's proprietary Mac OS X or Rhapsody-based operating systems. Binary releases of Darwin were available from Apple until Darwin 8.0, on which Mac OS X Tiger, version 10.4 from 2004, is based.