Storage device manufacturers measure capacity using the decimal system (base 10), so 1 gigabyte (GB) is calculated as exactly 1,000,000,000 bytes. The capacity of the storage media in your Mac, iPad, iPod, iPhone and other Apple hardware is measured using this decimal system. This is detailed on product packaging and online through the statement "1 GB = 1 billion bytes."
Understanding storage capacity in iPad, iPhone, iPod
When you view the storage capacity of your iPod, iPhone, iPad, or other electronic devices within its operating system, the capacity is reported using the the binary system (base 2) of measurement. In binary, 1 GB is calculated as 1,073,741,824 bytes.
For example: The way decimal and binary numeral systems measure a GB is what causes a 32 GB storage device to appear as approximately 28 GB when detailed by its operating system, even though the storage device still has 32 billion bytes (not 28 billion bytes), as reported.
You can see this difference if you look at how your computer summarizes the capacity of your iPod, iPad, or iPhones storage when the device is connected to your computer. You will also see this difference in the About menu on your iPod, iPad, or iPhone. The important point to understand is that the available storage capacity is the same no matter which system (decimal or binary) is used. Nothing is missing.
The storage media in your Apple product, like all storage devices, uses some of its capacity for formatting, so actual capacity available for applications and files will be less. In addition, other factors, such as pre-installed systems or other software and media, will also use part of the available storage capacity.
