Writing an application program would require a lot of work if you had only the device to work with. The good news is that the iOS framework uses a piece of software known as the operating system (OS), which provides device-independent interfaces to everything on the device (such as the file system, sensors, and so on). The OS also provides a standard interface to computing capabilities (such as for starting and stopping programs).
As a result, operating systems make writing and running applications easier, and they’re especially helpful — in fact, essential — on mobile devices. Apple developed and owns iOS, the operating system for its mobile products. Originally called the iPhone OS, iOS was unveiled in 2007 for the iPhone and was later extended to support the other Apple devices, as well as the Apple TV device.
Unlike, say, Linux, which powers Android and iOS is a single-user operating system. That said, this and other limitations are artificial. At its core, iOS can do nearly everything that Apple’s desktop operating system (OS X) can. For a variety of reasons, including secrecy and a genuine desire for tight quality control, Apple closely guards iOS, and only developers with special privileges are given access to its internals.
Devices
Every iOS device (like every mobile device) is a computer, composed of a set of hardware components: processor, memory, input/output (I/O) devices (such as a keyboard, touchpad, and screen), and storage (discs and flash, for example).
Unlike Android devices, the hardware configuration is controlled completely by Apple, so there are just four main variations of devices to consider when developing iOS apps:
✓ iPhone (of course)
✓ iPod Touch
✓ iPad
✓ iPad mini
Like other smart devices, iOS devices also come with several built-in hardware components, such as the following:
✓ Cameras (front and back facing)
✓ Audio inputs and outputs
✓ GPS
✓ Accelerometer
✓ Light sensor
Apple has yet to come out with a near-field communications-enabled device (or NFC-enabled device) but was recently awarded a patent for NFC-enabled data synching technology. For the inside story from Apple.
Unless you really and truly want to, you’ll never see iOS, the operating system, nor will your program. However, you must recognize that it’s there — the iOS framework does certain things in certain ways because it runs on iOS. For example, every running program is assigned a process. When an iOS app starts, an iOS process becomes active.
This process takes over an area of the screen on the device and allows the user to interact with the application. If another application starts, it pushes the first application to the background. At this point, the process assigned to the first application may be (arbitrarily) terminated by the operating system to save device resources. Before this happens, the iOS runtime notifies the application to save its state.
This iOS operating system is the OS that manages the device on which your apps run. A different operating system manages the personal computer on which you develop apps (the Macintosh OS or OS X).
