Android Boot Process

Clear, simple README explaining Android boot steps, design diagram, and how to use this repo.

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Overview

This document explains the Android boot process in simple words. It covers each step from power ON to system ready, explains what runs and why, and includes a simple diagram and suggested repo structure for a GitHub upload.

Keep the language simple so beginners can understand.

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Boot Steps (short summary)

1. Boot ROM (Power ON)

   • The device power turns on and Boot ROM code runs from a fixed location in ROM.
   • Boot ROM loads the bootloader into RAM and starts it.

2. BootLoader

   • Low-level code that prepares hardware and finds the kernel.

   • Runs in two stages:

     • Stage 1: Detect memory and load the stage-2 helper.
     • Stage 2: Initialize memory, network, and load the Kernel.

3. Kernel

   • The Linux kernel sets up memory, drivers, process table, and mounts root filesystem.
   • Kernel looks for the init process and starts it.

4. Init

   • The first user-space process (PID 1).
   • Mounts virtual filesystems like /sys, /proc, /dev and runs init.rc scripts.
   • Starts native services.

5. Zygote and Dalvik/ART VM

   • Zygote starts and preloads core Java classes and resources.
   • When an app launches, Zygote forks to create a new app process quickly.

6. System Server

   • System Server starts many Android services (ActivityManager, PackageManager, WindowManager, etc.).
   • When services are ready the system sends the ACTION_BOOT_COMPLETED broadcast.

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Detailed Design (for README)

Goals

• Explain each boot stage clearly.
• Provide a visual flow for learning and presentations.
• Provide a repo layout so code, diagrams, and notes are organized.

Visual Diagram (Mermaid)

flowchart LR
  A[Power ON] --> B(Boot ROM)
  B --> C(Bootloader)
  C --> D(Kernel)
  D --> E(Init)
  E --> F(Zygote / ART)
  F --> G(System Server)
  G --> H[ACTION_BOOT_COMPLETED]

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Note: GitHub supports Mermaid diagrams in Markdown. If your GitHub repo does not render it, add an image version in /docs/.

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Suggested Repository Structure

android-boot-process/
├─ README.md
├─ docs/
│  ├─ diagram.png        # optional image version of the diagram
│  └─ slides/            # optional presentation files
├─ notes/
│  └─ boot-details.md    # extra explanations and links
└─ LICENSE

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How to use this README

• Copy this README.md to the root of your GitHub repo.
• Add docs/diagram.png if you want an image that always renders on GitHub (some views don't render Mermaid).
• Add slides or PDFs to docs/slides if you plan to present.

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Short Explanations (one-line) for each term

• Boot ROM: First code that runs on power ON.
• Bootloader: Loads kernel and prepares hardware.
• Kernel: Core OS; handles drivers and system setup.
• Init: First user process that starts system services.
• Zygote: Java VM launcher that speeds up app start.
• System Server: Starts Android system services.

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License

Choose a license (for example MIT) and add a LICENSE file.

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Contributing

If you want to improve this README or add diagrams, open a PR. Keep explanations simple and add references for advanced reading.

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References & Further Reading

• Android source docs
• Linux boot process
• Android developer guides

Generated README template - edit as you like before uploading to GitHub.