The Anatomy of an iPad 2

The majority of coding that is involved in developing applications for the iPad consists of interacting with and responding to the device hardware in a variety of ways. Given this fact it is worth taking some time to look at the underlying hardware contains in the shell of an iPad. The focus of this overview will be the iPad 2 since this is the currently shipping device at the time of writing.

Before we delve into the hardware of the iPad we will start by talking about the operating system that sits on top of all the hardware. This operating system is called iOS 4 and is a variant of Apple’s Mac OS X operating system that was originally adapted to run on the iPhone and then subsequently used on the iPad. It is built upon a “UNIX-like” foundation called Darwin and consists of the Mach kernel, core services and media layers and the Cocoa Touch interface. iOS 4 is covered in greater detail in the chapter entitled iOS 4 Architecture and SDK Frameworks.

The iPad 2 has a 9.7 inch display with a resolution of 1024 x 768 pixels capable of displaying 132 pixels per inch (ppi) with an 800:1 contrast ratio. The underlying technology is an In Plane Switching (IPS) LED, capacitive touch screen. The screen has a scratch and oil and fingerprint resistant oleophopic coated surface. The device also has ambient light detection that adjusts the screen brightness to ensure the optimal screen visibility in a variety of lighting conditions from bright sunlight to darkness.

The iPad 2 supports a wide range of connectivity options. When within range of a Wi-Fi network, the device can connect at either 802.11b, 802.11g or 802.11n speeds.

For models with cellular support, the AT&T device supports GSM/EDGE connectivity (otherwise known as 2G). For faster speeds, support is also provided for connectivity via Universal Mobile Telecommunications System (UMTS), High-Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA). This is better known as 3G and provides data transfer speeds of up to 7.2 megabits per second. The Verizon model supports CDMA EV-DO Rev. A.

The iPad 2 also includes Bluetooth v2.1 support with Enhanced Data Rate (EDR) technology.

Given the wide array of wireless options it is not surprising that the iPad has little need for wired connections. In fact the iPad only has two. One is a standard 3.5 mm headset jack for the attachment of headphones or other audio devices. The second is a proprietary, 30-pin dock connector that, by default, is used to provide a USB v2.0 connection for synching with a computer system and battery charging. In practice, however, this connection also provides audio and TV output via specialty third party cables.

The iPad 2 comes in six configurations divided into WiFi only and WiFi + 3G categories. Each category of device is available in 16GB, 32GB and 64GB versions. The memory is in the form of a flash drive. Unlike some devices, the iPad lacks the ability to supplement the installed memory by inserting additional flash memory cards.

The iPad 2 contains both front and back facing cameras. The Back camera is capable of recording video at a resolution of 720p and at a rate of 30 frames per second and can also act a still camera with 5x digital zoom.

The front facing camera is VGA resolution also at 20 fps.

Sensors built into the iPad 2 consist of an accelerometer that uses the pull of gravity to detect when the device is moved or rotated, a three-axis gyroscope and an ambient light sensor that detects current environmental light levels.

All iPad 2 models contain a digital compass and the ability to identify approximate location information using WiFi. The WiFi + 3G models, however, also support location detection via GPS support with Assisted GPS (A-GPS) support. Essentially this enables the iPad to identify the current location by detecting radio signals from GPS satellites.

The central processing unit (CPU) of the iPad 2 is the Apple A5, an Apple designed 1Ghz dual core system-on-a-chip (SoC) consisting of an ARM Cortex A9 MPCore chip combined with an Imagination Technologies PowerVR Graphics Processing Unit (GPU). This Cortex A9 MPCore processor is designed by ARM Holdings, a British company that specializes in designing chips and then licensing those designs to third parties who then manufacture them. This differs considerably from the approach taken by companies such as Intel who both design and manufacture their own chips.

The Cortex A9 chip is based on the ARMv7 processor architecture and instruction set and was chosen by Apple for its combination of high performance and low power requirements.

As previously mentioned, iPad 2 graphics are handled by an Imagination Technologies PowerVR Graphics Processing Unit (GPU), specifically the PowerVR SGX 543MP2. This is provides support for OpenGL ES 1.1/2.0 (a lightweight version of SGI’s OpenGL platform), OpenGL 2.0/3.0 and OpenVG 1.1 and DirectX 9/10.1 graphics drawing and manipulation and includes the Universal Scalable Shader Engine (USSE), all key requirements for graphics intensive games development.

The iPad 2 includes both a built-in microphone and a speaker. Both the speaker and microphone may be used by third party apps, though as is to be expected with a device the size of an iPad, the sound quality of the speaker is widely considered to be poor.

The iPad 2 contains lithium-polymer battery rated at 25 watt hours and estimated to provide 9 - 10 hours of typical use including video or audio playback or WiFi internet access.

As we have seen in this chapter, the iPad 2 packs an impressive amount of technology into a case that is 9.5 inches high, 7.31 inches wide, 0.34 inches deep weighing in at 1.33 lbs. Perhaps the most exciting aspect of all this technology is that you can, almost without exception, access and utilize all this hardware within your own applications.