The iPhone keeps its iOS software -- the built-in programs that manage the touch screen, phone calls and other fundamental features -- in a special kind of memory chip that retains its data even without power. The combination of software and memory hardware is called firmware. Updates to the firmware, occasionally released by Apple, give the phone new capabilities.
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The iPhone, along with computers and other tech devices, uses different types of data storage memory. One type, called random access memory, is used for the short-term results of programs, such as variables in a calculation. RAM is written, erased and rewritten many times, and it is very fast; its contents change in less than a millionth of a second. Its main drawback is that it is volatile; when you turn the power off, the data disappears. Other kinds of memory, including flash, are slower but non-volatile. They are useful for storing information that doesn't change as often. Firmware, including that in the iPhone, is stored in non-volatile memory. If it were kept in volatile memory, all of the phone's programs and settings would vanish when you turned the power off, leaving you with a non-functioning device.
Programs and Data
Firmware contains both programs and data. Programs are sets of instructions executed by the iPhone's microprocessor that accomplish specific tasks; for example, the iPhone displays the home screen when you press the home button. The data firmware stores includes information such as iOS screen background graphics, iOS version number and the iPhone's basic ringtones.
The iPhone's flash memory can accept new information, allowing you to update the firmware when Apple releases a new version of iOS, for example. The rewritable nature of firmware in flash memory extend's an iPhone's useful lifetime, giving the device periodic "makeovers" that solve problems and add useful features.
The iPhone keeps a version number of its firmware in the Settings app. To view it, tap Settings, tap General, then tap About. Scroll down to Version to see the version number.
Restoring Factory Defaults
You can restore your iPhone to the state in which it came from the factory, removing all of your personal data and apps. This operation is essential before you sell your device, as it leaves no trace of your passwords, contacts or financial information. Restoring to factory defaults may also be necessary in extreme cases when an app has "locked up" or otherwise severely affected the iPhone. To restore your iPhone, connect it to a Mac or PC and start the iTunes program. In iTunes, click the iPhone device icon, click the Restore iPhone button, then click Restore again when the program asks if you're sure you want to proceed.
A process called jailbreaking, popular in the hacker community, replaces some of the iPhone's firmware with alternative software that allows greater customization of the phone as well as access to nonstandard apps. Jailbreaking, however, can void the Apple warranty, and loading apps that haven't gone through Apple's App Store validating process can expose your iPhone to viruses and malware.
Apple provides data files that contain a copy of your iPhone's firmware, for the purpose of updating the iPhone or restoring it to its factory default settings. Most iPhone owners never use these IPSW files, as the iOS update features in iTunes and in the iPhone's Settings app are more convenient and easy to use. However, for those owners who not have immediate access to high-speed Internet, it may be easier to download the particular IPSW file on another computer with a broadband Internet connection, copy the file to a PC or Mac and install it to the phone using iTunes.