computer science

Darwin (operating system)

Darwin (operating system) is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Darwin (operating system) rather than just read about it. In short: Darwin is the core Unix-like operating system of macOS, iOS, watchOS, tvOS, iPadOS, audioOS, visionOS, and bridgeOS. It previously existed as an independent open-source operating system, first released by Apple in 2000.

Key takeaways

Darwin (operating system) belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Darwin (operating system) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Darwin (operating system) from memory before moving on to harder problems.

Reference excerpt

Darwin is the core Unix-like operating system of macOS, iOS, watchOS, tvOS, iPadOS, audioOS, visionOS, and bridgeOS. It previously existed as an independent open-source operating system, first released by Apple in 2000. It is composed of code derived from NeXTSTEP, FreeBSD and other BSD operating systems, Mach, and other free software projects' code, as well as code developed by Apple. Darwin's unofficial mascot is Hexley the Platypus. Darwin is mostly POSIX-compatible, but has never, by itself, been certified as compatible with any version of POSIX. Starting with Leopard, macOS has been certified as compatible with the Single UNIX Specification version 3 (SUSv3).

History

The heritage of Darwin began with Unix derivatives supplemented by aspects of NeXT's NeXTSTEP operating system (later, since version 4.0, known as OPENSTEP), first released in 1989. After Apple bought NeXT in 1996, it announced it would base its next operating system on OPENSTEP. This was developed into Rhapsody in 1997, Mac OS X Server 1.0 in 1999, Mac OS X Public Beta in 2000, and Mac OS X 10.0 in 2001. In 1999, Apple announced it would release the source code for the Mach 2.5 microkernel, BSD Unix 4.4 OS, and the Apache Web server components of Mac OS X Server. At the time, interim CEO Steve Jobs alluded to British naturalist Charles Darwin by announcing "because it's about evolution". In 2000, the core operating system components of Mac OS X were released as open-source software under the Apple Public Source License (APSL) as Darwin; the higher-level components, such as the Cocoa and Carbon frameworks, remained closed-source. Up to Darwin 8.0.1, released in April 2005, Apple released a binary installer (as an ISO image) after each major Mac OS X release that allowed one to install Darwin on PowerPC and Intel x86 systems as a standalone operating system. Minor updates were released as packages that were installed separately. Darwin is now only available as source code. As of January 2023, Apple no longer mentions Darwin by name on its Open Source website and only publishes an incomplete collection of open-source projects relating to macOS and iOS.

Design

Kernel

The kernel of Darwin is XNU, a hybrid kernel which uses Open Software Foundation Mach Kernel (OSFMK) 7.3 from the OSF, various elements of FreeBSD (including the process model, network stack, and virtual file system), and an object-oriented device driver API called IOKit. The hybrid kernel design provides the flexibility of a microkernel and the performance of a monolithic kernel.

Hardware and software support The last bootable full release of Darwin supported 32-bit and 64-bit Apple PowerPC systems and 32-bit Intel PCs. Darwin currently includes support for the 64-bit x86-64 variant of the Intel x86 processors used in Intel-based Macs and the 64-bit ARM processors used in the iPhone 5S and later, the 6th generation iPod Touch, the 5th generation iPad and later, the iPad Air family, the iPad Mini 2 and later, the iPad Pro family, the fourth generation and later Apple TVs, the HomePod family, and Macs with Apple silicon such as the 2020 Apple M1 Macs, as well as the Raspberry Pi 3B. An open-source port of the XNU kernel exists that supports Darwin on Intel and AMD x86 platforms not officially supported by Apple, though it does not appear to have been updated since 2009. An open-source port of the XNU kernel also exists for ARM platforms, though it has not been updated since 2016. Older versions supported some or all of 32-bit PowerPC, 64-bit PowerPC, 32-bit x86, and 32-bit ARM. It supports the POSIX API by way of its BSD lineage (largely FreeBSD userland), so a large number of programs written for various other UNIX-like systems can be compiled on Darwin with no changes to the source code. Darwin does not include many of the defining elements of macOS, 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 macOS, such as mDNSResponder, which is the multicast DNS responder and a core component of the Bonjour networking technology, and launchd, an advanced service management framework.

License In July 2003, Apple released Darwin under version 2.0 of the Apple Public Source License (APSL), which the Free Software Foundation (FSF) qualifies as a free software license. The APSL is similar to AGPL, including in being incompatible with the GNU General Public License. Previous versions of the APSL license did not meet the FSF definition of free software, although they did meet the requirements of the Open Source Definition.

Release history The following is a table of major Darwin releases with their dates of release and their derivative operating system releases. Note that the corresponding releases may have been released on a different date.

Darwin 0–8 and corresponding Mac OS X releases

The jump in version numbers from Darwin 1.4.1 to 5.1 with the release of Mac OS X v10.1.1 was designed to tie Darwin to the Mac OS X version and build numbering system, which in turn is inherited from NeXTSTEP. In the build numbering system of macOS, every version has a unique beginning build number, which identifies what whole version of macOS it is part of. Mac OS X v10.0 had build numbers starting with 4, 10.1 had build numbers starting with 5, and so forth (earlier build numbers represented developer releases).

Darwin 9; iPhone OS introduced

Darwin 10-11; iPhone OS rebranded to iOS

Darwin 12–15; Mac OS X rebranded into OS X

Darwin 16–19; OS X rebranded into macOS

Darwin 20 onwards

Note: the tables above contain the release dates of the corresponding OS releases. Build dates for Darwin versions are not publicly available; the commands below only give the build date for the XNU kernel. The command uname -r in Terminal will show the Darwin version number ("20.3.0"), and the command uname -v will show the XNU build version string, which includes the Darwin version number. The command sw_vers will show the corresponding ProductName ("macOS"), the ProductVersion number ("11.2.3") and the BuildVersion string ("20D91").

Derived projects Due to the free software nature of Darwin, there have been projects that aim to modify the operating system or take Darwin’s parts for their own purpose. Among these, DarwinBSD, OpenDarwin, and PureDarwin can be termed "alternative Darwin distributions" in a sense analogous to Linux distributions.

OpenDarwin

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Darwin (operating system)

Start with the simplest possible case. Write down what Darwin (operating system) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Darwin (operating system) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Darwin (operating system) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Darwin (operating system)

In research: Darwin (operating system) appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Darwin (operating system) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Darwin (operating system) is common in secondary-school and first-year university syllabi. It links to neighbouring topics 2000 software, Animal mascots, Apple Inc. operating systems, so understanding it makes those chapters shorter.
In everyday life: Look for Darwin (operating system) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Darwin (operating system) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Darwin (operating system) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Darwin (operating system) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Darwin (operating system) in simple terms?

Why does Darwin (operating system) matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Darwin (operating system)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Darwin (operating system).