The Anatomy of an iPhone 4S

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Most books covering the development of apps for the iPhone tend to overlook the underlying hardware of the device and instead dive immediately into the software development environment. This is a shame because the iPhone is an incredible technical achievement that we are already starting to take for granted.

Take, for example, the iPhone 4S. This is a sleek device that is 115.2mm long, 58.6mm wide and 9.3 mm deep and weighs a mere 137 grams. Now, compare the size of your laptop or desktop computer to your iPhone. Then take a look at the specification for your computer and see if it has built in GPRS, EDGE and 3G wireless support, a digital compass, GPS, an accelerometer, a gyroscope, a proximity sensor, an ambient light sensor, Bluetooth capability, Wi-Fi, a multi-touch screen, a vibration generator and a 5 megapixel autofocus camera with built in flash and a second, 30 frame per second front facing camera. The chances are your much larger and heavier computer has only a small subset of these features. Next, check the expected battery life of your laptop and see if it will allow you to play music for 40 hours or video for 10 hours without needing a recharge. When you consider these capabilities you will hopefully begin to appreciate the engineering achievements behind the iPhone and other similar smartphone devices.

Now that we have set the scene, we can move on to discuss some of the hardware features built into the iPhone in a little more detail. Once again, we will do this within the context of the iPhone 5.

iOS 5

Before we delve into the hardware of the iPhone we will start by talking about the operating system that sits on top of all the hardware. This operating system is called iOS 5 and is a variant of Apple’s Mac OS X operating system which has been adapted to run on the iPhone. 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 5 is covered in greater detail in the chapter entitled iPhone iOS 5 Architecture and SDK Frameworks.


The iPhone 4S has a 3.5 inch display with a resolution of 960 x 640 pixels capable of displaying 326 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 oleophobic coated surface and includes a proximity sensor which automatically turns off the screen when you put the phone to your ear (presumably to extend the battery life during a phone call and to avoid making user interface selections with your ear). The device also has ambient light detection which adjusts the screen brightness to ensure the optimal screen visibility in a variety of lighting conditions from bright sunlight to darkness.

Wireless Connectivity

The iPhone 4S 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 making phone calls or transferring data when not connected to Wi-Fi, 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 iPhone 4S also includes Bluetooth v4.0 support with Enhanced Data Rate (EDR) technology.

Wired Connectivity

Given the wide array of wireless options it is not surprising that the iPhone has little need for wired connections. In fact the iPhone 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 which, 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 cables.


The iPhone 4S comes in three editions, containing 16GB, 32GB and 64GB of memory respectively. The memory is in the form of a flash drive. Unlike some devices, the iPhone lacks the ability to supplement the installed memory by inserting additional flash memory cards.


The iPhone 4S contains a 8 megapixel autofocus still camera which may also be used to record video at an HD resolution of 1080p included image stabilization and temporal noise reduction. In addition, the device also incorporates an LED flash and a VGA resolution, 30 fps front facing camera.


The latest generation of iPhone has an array of sensors which would make even the most die-hard 1960s science fiction fan jealous. These consist of a proximity sensor which detects when the front of the phone is covered or otherwise obscured, an accelerometer which uses the pull of gravity to detect when the device is moved or rotated, a three-axis gyroscope and an ambient light sensor to detect current environmental light levels.

Location Detection

The iPhone 4S contains a digital compass and GPS support with Assisted GPS (A-GPS) support. Essentially this enables the iPhone to detect the direction the device is facing and to identify the current location by detecting radio signals from GPS satellites. In the event that GPS signals are unavailable or too weak to establish the current coordinates, the iPhone can also gain an approximate location using cellular and Wi-Fi information.

Central Processing Unit (CPU)

The central processing unit (CPU) of the iPhone 4S is the Apple A5, an Apple designed system-on-a-chip (SoC) consisting of a dual core ARM Cortex A9 chip combined with dual core graphics processing unit (GPU). The Cortex A9 processor is designed by a British company named ARM Holdings which 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 which both design and manufacture their own chips.

Speaker and Microphone

As with most other phones on the market, the iPhone includes both a built-in microphone and a speaker to enable the use of the device as a speakerphone. 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 iPhone, the sound quality of the speaker is widely considered to be poor.


Though initially provided as a “silent ring” feature whereby the device vibrates to indicate an incoming call as an alternative to a ring tone (a feature common to most mobile phone devices), the vibration feature of the iPhone may also be used within applications to notify the user of a new event (such as a breaking news story) or to provide tactile feedback such as for an explosion in a game.


As we have seen in this chapter, the iPhone packs an impressive amount of technology into a very small amount of space. 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.

Purchase the fully updated iOS 12 / Xcode 10 edition of this book in eBook format for only $24.99.
iOS 12 App Development Essentials eBook (ePub/PDF/Kindle) edition contains over 120 chapters. Learn more...

Buy Print Preview Book

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About iPhone iOS 5 Development EssentialsiPhone iOS 5 Architecture and SDK Frameworks