Getting Started with iOS Development Part6:iOS Scripting iOS Hardware Guide

iOS Hardware Guide

Hardware models

Following table summarizes iOS hardware available in devices of various generations:

Common to all iOS devices

• Screen: 320x480 pixels, LCD at 163ppi (unless stated otherwise)
• Built-in accelerometer
• Wi-Fi

Original iPhone

• ARM11, 412 Mhz CPU
• PowerVR MBX Lite 3D graphics processor
• 128MB of memory
• 2 megapixel camera
• Speaker and microphone
• Vibration support
• Silent switch

iPhone 3G

• GPS support

iPhone 3GS

• ARM Cortex A8, 600 MHz CPU
• PowerVR SGX graphics processor
• 256MB of memory
• 3 megapixel camera with video capture capability
• Compass support

iPhone 4

• ARM Cortex-A8 Apple A4 CPU
• ARM Cortex-A8 Apple A4 graphics processor
• 512MB of memory
• Cameras
  • Rear 5.0 MP backside illuminated CMOS image sensor with 720p HD video at 30 fps and LED flash
  • Front 0.3 MP (VGA) with geotagging, tap to focus, and 480p SD video at 30 fps
• Screen: 960x640 pixels, LCD at 326 ppi, 800:1 contrast ratio.
• Vibration Support
• Compass Support

iPod Touch 1st generation

iPod Touch 2nd generation

• ARM11, 533 Mhz CPU

iPad

• 1 GHz Apple A4 CPU
• Wifi + Blueooth + (3G Cellular HSDPA, 2G cellular EDGE on the 3G version)
• Accelerometer, ambient light sensor, magnetometer (for digital compass)
• Mechanical keys: Home, sleep, screen rotation lock, volume.
• Screen: 1024x768 pixels, LCD at 132 ppi, LED-backlit.

Graphics Processing Unit and Hidden Surface Removal

The iPhone/iPad graphics processing unit (GPU) is a Tile-Based Deferred Renderer. In contrast with most GPUs in desktop computers, the iPhone/iPad GPU focuses on minimizing the processing required to render an image as early in the processing of a scene as possible, so that only the pixels that actually will be seen consume processing resources.

The GPU's frame buffer is divided up into tiles and rendering happens tile by tile. First, triangles for the whole frame are gathered and assigned to the tiles. Next, visible fragments of each triangle are chosen. Finally, the selected triangle fragments are passed to rasterizer (triangle fragments occluded from the camera are rejected at this stage).

In other words iPhone/iPad GPU implements Hidden Surface Removal operation at reduced cost. Such architecture consumes less memory bandwidth, has lower power consumption, and utilizes texture cache better. Tile-Based Deferred Rendering allows the device to reject occluded fragments before actual rasterization which is effective to keep overdraw low.

For more information see also:

• POWERVR MBX Technology Overview
• Apple Notes on iPhone/iPad GPU and OpenGL ES
• Apple Performance Advices for OpenGL ES in General
• Apple Performance Advices for OpenGL ES Shaders

SGX series

Starting from iPhone 3GS and newer devices are equipped with SGX series of GPUs. SGX series features support for OpenGL ES2.0 rendering API, vertex and pixel shaders. Fixed-function pipeline is not supported natively on such GPUs, instead it is emulated by generating vertex and pixel shaders with analogous functionality on the fly.

SGX series fully supports MultiSample anti-aliasing.

MBX series

Older devices such as iPhone, iPhone 3G, iPod Touch 1st and 2nd Generation are equipped with MBX series of GPUs. MBX series supports only OpenGL ES1.1, fixed function Transform&Lighting pipeline and 2 textures per fragment.

Texture Compression

The only texture compression format supported by iOS is PVRTC. PVRTC provides support for RGB and RGBA (color information + alpha channel) texture formats and can compress single pixel to 4 or 2 bits.

PVRTC format is essential to save memory footprint and to reduce consumption of memory bandwidth (rate at which data can be read from memory, usually very limited on Mobile devices).

Vertex Processing Unit

Unified Memory Architecture

Multimedia CoProcessing Unit