The iPhone is a cell phone manufactured by Apple that plays music, shoots pictures and videos and can connect to the Internet over cell phone data networks and Wi-Fi. The iPhone can also run "apps" or applications. Each application must load in the iPhone's memory before you can use it. If too many memory-intensive apps are running at the same time, one or more of the applications may shut down without warning.
Memory on the iPhone
The iPhone 4 has 512 megabytes of random access memory (RAM), which is where applications load and run. This memory is separate from the phone's storage capacity, which holds music, videos, pictures and apps. The iPhone 4 comes with either 16 or 32 gigabytes of this system memory. Certain apps can consume greater amounts of memory as you use them. For example, the Safari web browser can open up to eight pages at once. If these multiple open pages require a lot of memory, another application, such as music or video playback with the iPod app, may suddenly close down.
The iOS4 operating system allows the iPhone to run multiple applications simultaneously. For example, you can browse the Web with Safari while listening to music with the iPod app. If an app is designed to take advantage of iOS4's multitasking, it usually will hibernate when you are not using it. It only requires enough memory to store its current state, so you can switch back to it quickly from another application.
If you want to fully quit an application instead of just switching to another one, double-click on the "Home" button. This will bring up the four most recently used apps in the task bar at the bottom. Flick the screen left to see more recently used apps. Touch an app's icon until it starts jiggling; a red circle with a white minus sign will appear on it and the other apps in the task bar. Tap the red circle to close that app and free up some memory. If you have eight pages open in Safari, try closing the ones you are no longer interested in browsing.
Monitor Memory Use
You can download applications from Apple's App Store that will tell you how memory is being used by different applications (see Resources). For example, iStat, Free Memory and Memory Status will display statistics about currently running apps, with pie chart views showing the ones hogging the most memory. Some memory monitoring apps also allow you to terminate an application to free up memory and enable other apps to run more efficiently.
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