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Darwin is a free and open source, Unix-like operating system first released by Apple Inc. in 2000. It is a standalone operating system as well as the core set of components upon which Mac OS X was developed. It is primarily developed by Apple to support Mac OS X.
Darwin can trace its heritage back to NeXT's NEXTSTEP operating system (later known as OPENSTEP), originally released in 1989. After Apple's 1997 acquisition of NeXT, the company announced it would use OPENSTEP as the basis for its next operating system. This was developed into Rhapsody in 1997 and the Rhapsody-based Mac OS X Server 1.0 in 1999. In 2000, Rhapsody was forked into Darwin and released as open-source software under the Apple Public Source License (APSL).
Darwin is built around XNU, a hybrid kernel that combines the Mach 3 microkernel, various elements of FreeBSD 5 (including the process model, network stack, and virtual file system), and an object-oriented device driver API called I/O Kit.[1]
Some of the benefits of this choice of kernel are the Mach-O binary format, which allows a single executable file (including the kernel itself) to support multiple CPU architectures, and the mature support for symmetric multiprocessing in Mach. The hybrid kernel design compromises between the flexibility of a microkernel and the performance of a monolithic kernel.
Darwin currently includes support for PowerPC and Intel x86 processors.
Darwin does not include many of the defining elements of Mac OS X, such as the Carbon and Cocoa APIs or the Quartz Compositor and Aqua user interface, and thus cannot run Mac applications. It does, however, support a number of lesser known features of OS X, such as mDNSResponder, the multicast DNS responder and a core component of the Bonjour networking technology, and launchd, an advanced service management framework.
It also supports the POSIX API by way of its FreeBSD lineage and can run a large number of programs written for various other Unix-like systems.
Darwin and OS X both use I/O Kit for their drivers and therefore support the same hardware, file systems, and so forth. Apple's distribution of Darwin includes binary-only (closed-source) drivers for their AirPort wireless cards.
In July 2003, Apple released Darwin under version 2.0 of the APSL license, which the Free Software Foundation (FSF) approved as a free software license. Previous releases had taken place under an earlier version of the APSL that did not meet the FSF's definition of free software, although it met the requirements of the Open Source Definition.
The Darwin developers decided to adopt a mascot in 2000, and chose Hexley the platypus over other contenders, such as an Aqua Darwin fish, Clarus the dogcow, and an orca. Apple does not sanction Hexley as a logo for Darwin.
This is a table of Darwin releases with their dates of release and their corresponding Mac OS X releases.[2] Note that the corresponding Mac OS X release may have been released on a different date; refer to the OS X pages for those dates.
Notice that the version number jumps from Darwin 1.4 to 5. The two versioning systems have different stories. Initially, Apple established the 1.x designation, in order for Darwin version numbers to correspond to the Mac OS X Server 1.x version numbers. However, the Mac OS Server 1.x saw limited use and that versioning practice was discontinued even before Mac OS X was widely introduced. The Darwin 5.x designations, on the other hand, continue the NEXTSTEP versioning (which left off at NEXTSTEP 3.3, followed by OPENSTEP (which later became Darwin), at 4.2). Since the prepackaged "Darwin 1.x" distribution was actually created based on the Darwin 4 code underlying the Mac OS X, Apple decided to ease confusion and to continue with the version numbers it inherited when it bought NEXTSTEP. The command <tt>uname -r</tt> in Terminal will show the Darwin version number, and the command <tt>uname -v</tt> will show the XNU build version string, which includes the Darwin version number.
Apple releases a Darwin installer ISO image after each major Mac OS X release. Minor updates are released as packages that must be installed separately.
Due to the free software nature of Darwin, there are many projects that aim to modify or enhance the operating system: