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kconner/macOS Internals.md

Last active May 7, 2023 23:00

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macOS Internals.md

 macOS Internals

Understand your Mac and iPhone more deeply by tracing the evolution
of Mac OS X from prelease to Swift. John Siracusa delivers the
details.

 Starting Points

 How to use this gist

You've got two main options:

 1. Under Highlights, read all the links you're interested in, or
 2. Use "OS X Reviewed" as an index and just read all the reviews end
    to end. (This is not the fast option, but it inspired me to
    gather all these highlights.)

In either case, to get the greatest benefits of context and
intuition, I recommend that you read in chronological order.

 OS X Reviewed

    Nearly 15 years ago, I wrote my first review of Mac OS X for a
    nascent "PC enthusiast's" website called Ars Technica. Last fall,
    I wrote my last.

 Highlights

These chronologically-ordered highlights jump into the middle of
long, paginated articles. Topics often span a few pages, so look for
the "Next Page" links.

 Quartz 2D: PDF-based drawing

    I've chosen to define the three generations of display layer
    technology in order to illustrate the most important changes over
    the years.

 Packaged Applications and Frameworks

    The three main "subspecies" of Bundles are Application Packages,
    Frameworks, and Loadable Bundles.

 The Window Server

    It has two main responsibilities: Event routing, and composing
    and displaying on-screen elements.

 Project Builder, better known as Xcode

    What may not be so obvious is that Project Builder is built on
    top of popular open source development tools: everything from
    gcc, gdb, and cvs to smaller tools like diff.

 Memory on macOS

    Mac OS X manages memory very differently than classic Mac OS. The
    first key to understanding memory usage in Mac OS X is to be
    understand how a modern virtual memory system works.

 Rendezvous, now known as Bonjour and Zeroconf

    Rendezvous enables a local network of devices to configure
    themselves without the aid of any centralized servers.

 GPU-accelerated display compositing

    It's slightly confusing to think about the window server as an
    OpenGL application, but that's what it is.

 "Sherlocking"

    As the Watson FAQ explains, although Apple's new version of
    Sherlock is a dead-ringer for Watson, there is no formal
    relationship between the two applications.

 Spatial window management and Expose

    Panther includes a new window management feature that effectively
    increases the size of your screen by shrinking all of your
    windows temporarily. Following Apple's recent Gallic naming
    trend, it's called Expose.

 launchd

    One launch daemon to rule them all.

 Extended file attributes

    Mac OS X now includes support for arbitrarily extensible file
    system metadata.

 Spotlight

    Spotlight is a system service that accepts a query and returns
    all file system objects (files and folders) that match the query.

 GPU-accelerated window drawing

    The only thing left for the CPU to do is to send (relatively
    tiny) drawing commands to the video card through the driver.

 DTrace and Instruments

    This application was called Xray for most of its development
    life, which explains the icon. It's now called Instruments for
    reasons that surely involve lawyers.

 FSEvents

    To be aware of all relevant file system changes, the notification
    mechanism must exist at the choke point for all local i/o: the
    kernel. But the kernel is a harsh mistress, filled with draconian
    latency and memory restrictions.

 Core Animation

    Core Animation's original name, Layer Kit, reveals a lot about
    its design. At its heart, Core Animation manages a collection of
    2D layers.

 Time Machine

    "I know I should back up, but I never do. I wouldn't even know
    how to do something like that anyway." Well, enough of that.

 LLVM, Clang, and Objective-C Blocks

    By committing to a Clang/LLVM-powered future, Apple has finally
    taken complete control of its development platform.

 GCD: Grand Central Dispatch

    The bottom line is that the optimal number of threads to put in
    flight at any given time is best determined by a single, globally
    aware entity.

 The Recovery Partition

    The new partition is actually considered a different type:
    Apple_Boot. The Recovery HD volume won't be automatically mounted
    upon boot and therefore won't appear in the Finder.

 Hidden scroll bars and natural scroll direction

    Lion further cements the dominance of touch by making all
    touch-based scrolling work like it does on a touchscreen.

 Modernized Document Model

    At this point, a little bit of "geek panic" might be setting in.

 Automatic Termination

    Whereas Sudden Termination lets an application tell the system
    when it's okay to terminate it with extreme prejudice, Automatic
    Termination lets an application tell the system that it's okay to
    politely ask the program to exit.

 App Sandboxing and Entitlements

    A sandboxed application must now include a list of "entitlements"
    describing exactly what resources it needs in order to do its
    job.

 ARC: Automatic Reference Counting

    There is no process that scans the memory image of a running
    application looking for memory to deallocate. Everything ARC does
    happens at compile time.

 FileVault whole disk encryption

    This encryption is completely transparent to all software
    (including the implementation of HFS+ itself) because it takes
    place at a layer above the volume format.

 Document revision storage

    Unlike earlier incarnations of autosave, you won't see
    auto-generated files appearing and disappearing alongside the
    original document. But the data obviously has to be stored
    somewhere, so where is it?

 iCloud

    Apple provides three different kinds of iCloud data storage APIs,
    with very little overlap between them in terms of functionality
    and intended purpose.

 Gatekeeper, code signing, and quarantine

    Gatekeeper is the latest stop in Apple's long, ongoing journey
    toward a more secure, worry-free computing experience on the Mac.
    Once again, iOS is the model.

 Objective-C 2.0 syntax

    Even if you have no idea what any of that means, I believe you
    may still find the table below compelling.

 Power Nap

    In this mode, the audio and graphics systems remain powered down,
    but the disk, CPU, and networking hardware are all active.

 Finder Tags

    Labels were introduced way back in System 6 in 1988. Since Apple
    made both the Finder and the file system, it reserved a place in
    the file system metadata for what it called "Finder Info."

 App Nap and Background Tasks

    By coalescing the work into a contiguous burst of high activity,
    transitional waste has been cut to a bare minimum, and the amount
    of idle time has been maximized.

 Compressed Memory

    Like the HFS+ compression feature introduced in Snow Leopard,
    compressed memory trades relatively abundant CPU cycles for
    decreased disk I/O.

 iCloud Drive

    Replacing the existing iCloud document storage is the new iCloud
    Drive--and I do mean replacing.

 App Extensions

    Though they are distributed inside an application's bundle,
    Extensions are not just applications launched in a special mode.
    They are separate, purpose-built binaries, with their own
    containers, code signatures, and entitlements.

 Handoff

    When all the dots connect, it really is a neat experience. Now
    let's talk about those dots.

 Swift

    Perhaps this mission statement is so grandiose--so preposterous,
    even--that readers are inclined to gloss over it or dismiss it.
    But it's the key to understanding the design of Swift.

@kconner
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kconner commented May 7, 2023 *
edited

Lobste.rs discussion, 20 May 2023
Hacker News discussion, 22 May 2023

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