A gigabyte is a measure of storage on a computer memory chip, a peripheral device such as a hard drive or flash drive, or the media used in these drives such as CD and DVD optical discs. One gigabyte, abbreviated GB, is equal to one billion bytes. Apple's iPhone 4 can be purchased with 16 or 32 gigabytes of on-board memory for storing multimedia files such as music, videos and voice mail as well as applications. You can view the amount of gigabytes on your iPhone and find out how much of this memory is available to you for storage through the iPhone's "Settings" menu.
Tap on the "Settings" application on your iPhone. This app is factory-installed on all iPhones.
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Tap on "General" from the Settings menu.
Tap on "About" from the General menu.
Scroll down the page to the "Capacity" section. Here you will see the amount of memory installed on your iPhone, expressed in gigabytes.
Scroll down to the "Available" section. The number you see here indicates how many unused gigabytes of storage are available on the iPhone. If you are running low on space, you can delete some photos, videos, songs or applications to free up more memory.
Press the "Home" button, located below the iPhone's screen, to exit the Settings application.