OS

Android Architecture: Revision Notes

1. Application Framework:

• Developer Use: Primarily used by application developers.

• Hardware Developer Awareness: Developer APIs often map directly to underlying HAL interfaces, providing helpful information for implementing drivers.

2. Binder IPC:

• Mechanism: Allows application framework to cross process boundaries and interact with Android system services.

• Hidden Communication: At the application framework level, communication is hidden from the developer, making things appear seamless.

3. System Services:

• Functionality: Application framework APIs communicate with system services to access hardware.

• Modular Services: Includes components like Window Manager, Search Service, Notification Manager.

• Service Groups:

• System services (e.g., Window Manager, Notification Manager).

• Media services (e.g., playing and recording media).

4. Hardware Abstraction Layer (HAL):

• Standard Interface: Defines a standard interface for hardware vendors, allowing Android to be agnostic about lower-level driver implementations.

• Modular Implementation: HAL implementations are packaged as modules (.so files) and loaded dynamically.

• Custom Implementation: Developers must implement HAL and driver for their specific hardware, adhering to hardware-specific HAL interfaces.

5. HAL Modules:

• Implementation: Built into modules (.so files), dynamically linked by Android.

• Building Modules: Use Android.mk files for each HAL implementation, pointing to source files.

• Naming Scheme: Shared libraries must follow a specific naming pattern: <module_type>.<device_name>.

6. Linux Kernel:

• Driver Development: Similar to developing typical Linux device drivers.

• Special Additions: Android uses a modified Linux kernel with additions like wake locks, Binder IPC driver, and other mobile-specific features.

• Kernel Version: Any kernel version can be used if it supports required features like the binder driver.

iOS Architecture: Revision Notes

1. Core OS Layer:

• Foundation Layer: Manages memory, file systems, networking, and other OS tasks.

• Hardware Interaction: Directly interacts with the hardware.

2. Core Services Layer:

• Abstraction: Provides fundamental access to iOS services over the Core OS layer.

• Components:

• Collections: Data management and service features.

• Address Book: Access to user's contacts.

• Networking: Determines network availability and state.

• File Access: Access to lower-level OS services.

• SQLite: Embedded SQL database.

• Core Location: Determines device location and orientation.

• Net Services: Determines network connection and server accessibility.

• Threading, Preferences, URL Utilities: Data management and service features.

3. Media Layer:

• Multimedia Services: Provides services for audio, video, and image handling.

• Components:

• Core Audio: Playback and recording of audio.

• OpenGL/OpenGL ES: 2D and 3D animations.

• Audio Mixing/Recording: Mixes system announcements with background audio and records sound.

• Video Playback: Plays video using MPMoviePlayerController.

• Image Formats: Interfaces for JPG, PNG, TIFF.

• PDF: Text layout and rendering.

• Quartz: Image and video processing, animations.

• Core Animations: Advanced support for animating views.

4. Cocoa-Touch Layer:

• Abstraction Layer: Provides libraries for iPhone and iOS device programming.

• Multi-Touch Support: Located at the top due to Multi-Touch capabilities.

• Components:

• Multi-Touch Events: Detects taps, swipes, pinches, etc.

• Multi-Touch Controls: Responds to multi-finger touch actions.

• View Hierarchy: Model-View-Controller pattern management.

• Alerts: Communicates errors or requests input using UIAlertView.

• People Picker: Displays contact details from AddressBook.

• Controllers: Manages basic application behaviors and view reorientation.

• Accelerometer/Gyroscope: Measures device motion and rotation.

• Localization/Geographical: Adds maps and satellite images.

• Web Views: Embeds web content and displays HTML.

• Image Picker: Multi-dimensional user-interface element.

BlackBerry 10 Architecture: Revision Notes

1. CPU Embedded Bootloader:

• Digital Signature Verification: Verifies the digital signature of the bootloader code before execution.

2. Bootloader:

• OS Signature Verification: Verifies the digital signature of the OS before it runs.

3. Microkernel:

• Minimal OS Software: The essential software required for the OS to function.

4. Radio:

• Drivers and Services: Includes drivers, stacks, and services to support radio subsystems for voice, data, and other services.

5. Drivers and BSP (Board Support Package):

• Hardware Support: Contains drivers and board initialization logic to support the device hardware.

6. OS:

• Kernel-External Processes: Processes that operate outside of the kernel.

7. Platform and Application Services:

• Background Services: Includes security management, software installation and management, media services, and more.

• Service Isolation: Ensures apps cannot run background services or access protected system components directly.

8. Application Runtimes:

• Isolated Sandboxes: All applications run in isolated environments.

• Supported Platforms: Supports native SDK, Android, and HTML5 applications.

9. Apps:

• Preloaded and Installed Applications: Includes preloaded, user-installed, and organizationally deployed apps.

OS Comparison: Revision Notes

Windows OS:

• Architecture:

• User Mode: Less privileged, uses APIs for system services, no direct hardware access.

• Kernel Mode: Privileged, direct hardware/memory access, three components: Windows Executive, Kernel, HAL.

• Features:

• User-friendly interface, extensive application support.

• Strong integration with Microsoft services.

• Suitable for desktop and server environments.

Linux OS:

• Architecture:

• Kernel: Core component, interacts with hardware, provides low-level services.

• System Library: Accesses kernel features, implements OS functionalities.

• System Utility: Specialized programs for individual tasks.

• Features:

• Open source, portable, multi-user, multiprogramming.

• Hierarchical file system, shell for command execution.

• Strong security through authentication and encryption.

Mac OS:

• Architecture:

• Darwin Core: Comprises Mach, BSD, and I/O Kit.

• Mach: Manages CPU, memory, IPC, and real-time services.

• BSD: Provides file systems, networking, UNIX security, and POSIX APIs.

• I/O Kit: Framework for device drivers, modular and extensible.

• Features:

• User-friendly interface, strong multimedia capabilities.

• Seamless integration with Apple ecosystem.

• High stability and security, UNIX-based.

Android OS:

• Architecture:

• Linux Kernel: Modified for mobile use, includes wake locks and Binder IPC.

• HAL (Hardware Abstraction Layer): Standard interface for hardware vendors.

• System Services: Modular components like Window Manager and Notification Manager.

• Application Framework: APIs for app development.

• Apps: User-installed or preloaded applications.

• Features:

• Open source, highly customizable.

• Extensive app ecosystem, strong Google integration.

• Suitable for smartphones and tablets.

iOS:

• Architecture:

• Core OS Layer: Foundation, manages memory, file system, and networking.

• Core Services Layer: Abstraction over Core OS, includes collections, address book, networking, SQLite, etc.

• Media Layer: Multimedia services (audio, video, graphics).

• Cocoa-Touch Layer: Multi-touch events, view hierarchy, controllers, and more.

• Features:

• Secure, smooth performance.

• Extensive app ecosystem, strong Apple ecosystem integration.

• Consistent user experience, robust multimedia capabilities.

BlackBerry 10:

• Architecture:

• CPU Embedded Bootloader: Verifies bootloader code.

• Bootloader: Verifies OS code.

• Microkernel: Minimal software for OS operation.

• Radio: Drivers for radio subsystems.

• Drivers and BSP: Hardware support.

• OS: Kernel-external processes.

• Platform and Application Services: Security, installation, background services.

• Application Runtimes: Sandboxed environments for native, Android, and HTML5 apps.

• Apps: Preloaded, user-installed, or organization-deployed apps.

• Features:

• Strong security and enterprise features.

• Supports multiple app platforms.

• Focused on productivity and communication.

Windows Phone:

• Architecture:

• Similar to Windows OS: User mode and kernel mode separation.

• Adapted for mobile use: Includes mobile-specific optimizations.

• Features:

• Seamless integration with Microsoft services and ecosystem.

• User-friendly interface.

• Limited app ecosystem compared to Android and iOS.