Zygote
Android 17 · API 37 · 194 pages · 32 modules

Everythingbetween the tapand the pixel.

Android is a stack of about twenty layers, and almost nobody sees all of them at once. Zygote does. One continuous explanation of the operating system — from the Linux kernel and the vendor interface, through Binder and the runtime, to Compose and the frame that reaches your eyes.

Start readingThe whole journey in one page

Every layer below is clickable.

Your appskotlinSystem appsprivilegedFrameworksystem_serverRuntimeARTNativeC++HALvendorKernelLinuxcalls
The map

Everything, in the order a machine actually works

The modules are not alphabetical. They follow the stack: what runs first, what it calls, and what breaks when you change it. Start anywhere, but the prerequisites on each page tell you what you are missing.

Start here

What Zygote is, and the shape of the whole machine.

4 pages · 36 minStart hereWhat Zygote is, how the four layers work, and how to read the site.4 interactive

How Android works

The platform from silicon to system_server. This is the spine of the site.

4 pages · 39 minThe big pictureDraw Android's whole stack from memory, and see one tap cross every layer.4 interactive4 pages · 62 minThe Linux kernelThe engine under everything — and what Android bolted onto it.4 interactive4 pages · 58 minBootFrom a press of the power button to a home screen, step by step.4 interactive5 pages · 59 minBinder & IPCHow a hundred sandboxed processes talk without trusting each other.5 interactive6 pages · 68 minZygote, Dalvik & ARTWhy every app is a copy of one process, and how your Kotlin actually executes.6 interactive6 pages · 74 minsystem_serverOne process, a hundred services, and almost everything you call.6 interactive6 pages · 72 minHALs, Treble & MainlineThe decade-long project to make Android updatable.6 interactive8 pages · 93 minSecurityDefence in depth, from the hardware root of trust to your app's sandbox.8 interactive6 pages · 74 minGraphicsChromium-free rendering: how a frame gets from your code to your eyes.6 interactive6 pages · 72 minInput & windowsFrom a touch digit to a click handler, and how windows stack.6 interactive5 pages · 60 minMemory, lifecycle & powerWhy Android kills apps on purpose, and how it rations the battery.5 interactive5 pages · 57 minStorageFrom the wild west of /sdcard to scoped storage.5 interactive5 pages · 58 minConnectivity, location & sensorsRadios, sockets, satellites and a chip that tells you which way is down.5 interactive5 pages · 55 minMedia, audio & cameraDecoding, playing, capturing, and the vulnerability that changed Android.5 interactive5 pages · 52 minAPKs & installationWhat is actually inside an APK, and what happens when you install one.5 interactive

How apps work

What happens inside the code you write, and why the platform shaped it.

8 pages · 88 minComponents & IntentsWhy Android apps have no main(), and the four ways in.8 interactive5 pages · 55 minThreads & concurrencyOne main thread, a clever message queue, and twenty years of async.5 interactive7 pages · 77 minUI toolkitsViews, Compose, and the machinery between your state and the screen.7 interactive7 pages · 77 minApp architectureFrom the God Activity to unidirectional data flow.7 interactive4 pages · 47 minJetpackMost of the "Android API" you use today isn't in the OS.4 interactive5 pages · 59 minThe build systemWhat ./gradlew assembleRelease actually does.5 interactive4 pages · 44 minJava to KotlinWhy Android chose Java, escaped it, and fell for Kotlin.4 interactive5 pages · 57 minBackground workThe long war between apps that want to run and batteries that die.5 interactive4 pages · 47 minPrivacyHow Android learned to say no, one release at a time.4 interactive4 pages · 46 minNotifications & SystemUIThe shade, the status bar, and the launcher that is just an app.4 interactive

How it evolved

Twenty years of Android, version by version, and the tools to explore it.

4 pages · 50 minEvolutionThe Time Machine, every version, and the API explorer.4 interactive

Curiosity

The odd corners, the myths, and the people.

5 pages · 60 minCuriosityMyths corrected, easter eggs found, and the origin story.5 interactive

Hands-on

Labs, source tours, and projects you can actually build.

5 pages · 60 minAOSP source tourLearn to read the real source, with ten guided quests.5 interactive14 pages · 83 minHands-on labsPoke at a real device. Nine labs, then five tracing labs.2 interactive21 pages · 89 minBuilder trackReal Android projects that make each concept tangible.2 interactive

Study

Paths, quizzes, flashcards, and cheat sheets.

8 pages · 49 minStudyPaths, quizzes, flashcards, cheat sheets and the concept map.8 interactive
The instruments

Four ways to explore that no article can give you

The Time MachineDrag a slider from API 1 to 37 and watch the whole platform change: the architecture, the design language, the APIs and what a developer had to do.The API ExplorerEvery public class, method and field, with the level it was added and deprecated. Search it, chart its growth, or visit the graveyard.The Concept MapThe whole site as one graph. See how Binder reaches system_server, AIDL and Treble, and find the shortest path between any two ideas.The LabsFourteen hands-on labs on a real device or emulator. See the zygote in `ps`, read an ANR trace, and trace a frame with Perfetto.
Wait, really?

Ten seconds of curiosity

Small, sourced facts that are more interesting than they have any right to be. There are 207 in the cabinet.

Why did alarms become inexact by default?Because exact alarms wake the device at a specific moment, which is expensive when many apps do it. Batching alarms into wake windows saves battery. Exact alarms are still available, but they now require a permission and a justification.backgroundbatteryHow can you see exactly what changed in an API level?The API diff reports on developer.android.com list every class, method and field added, changed or removed between two levels. They are generated from the SDK itself, so they are the most precise record of the public surface changing.evolutionWhy is there more than one Zygote?Isolated processes need a different security context and a different startup path, so Android has an app zygote to fork them. It also avoids loading the full app class set into those processes, which keeps them lean.runtimesecurity
Open the Curiosity Cabinet → 207 cards
Where to begin

Three doors

Never written an appThe Curious BeginnerNo code required. Start with the trailer page, then boot, processes, security and the privacy story. About four hours.Start the path →You build appsApp Developer FoundationsComponents, lifecycle, threading, UI, architecture and Jetpack — the why behind the APIs you already use.Start the path →You want the sourceThe Platform NerdKernel, boot, Binder, ART, system_server, Treble — and ten reading quests through the real AOSP tree.Start the path →

How we handle being wrong

Every claim has a source

Version numbers, API levels, class names and dates are traced to a primary source — AOSP documentation, the Android developer site, the actual source tree, or a launch blog post. The numbered superscripts on each page point at the list.

Uncertainty is visible

Where we could not confirm something against a primary source, the sentence is marked like this. It is never quietly smoothed over. A thinner correct page beats a rich invented one.

Pages carry a date

Each page shows when its facts were last checked. Android changes every year, and a page that does not tell you its age is a page you cannot trust.