iPhone 4S storage capacity doesn’t match

Q: I believe that Apple is counting the 5 GB iCloud allocation as part of the 64 GB total storage on my shiny new 4S since it actually only comes with 57GB—not 64 GB as advertised. That is unless the iOS 5 actually requires 7 GB of space. The only problem with the 5 GB in the cloud is that for folks like myself who prefer to keep photos and documents on a separate hard drive, it’s pretty much useless space as you are unable to choose what may be stored, outside of the set parameters. I’d be interested in finding out if I am correct.

– Al

A: Actually, the 5GB of iCloud storage has nothing to do with it. What you’re actually seeing here is a long-standing problem between how data storage is measured by hardware manufacturers versus software manufacturers. Essentially, since computer software is based on binary storage, which uses factors of two, a kilobyte is not actually 1,000 bytes, but 1,024 bytes. By extension, a megabyte is 1,024 kilobytes (or 1,048,576 bytes), a gigabyte is 1,024 megabytes (1,073,741,824 bytes), and so on.

By comparison, hardware manufacturers have been using the decimal values for years (kilo=1000, mega=1,000,000, etc), and this applies to everything from computer hard drives to flash memory cards to the storage in iPods and iPhones and other electronic devices. To a flash memory chip manufacturer, a 64GB memory chip stores 64,000,000,000 bytes, whereas to computer software, a 64GB memory chip should store 68,719,476,736 bytes.  Ergo, a 64GB (64,000,000,000 byte) memory chip is actually only 59.6 GB as far as the software is concerned. Add the overhead for iOS itself—which is actually stored in a separate partition—- and that leaves about 57.4 GB free.

This problem is not unique to iOS devices or even Apple. Every storage manufacturer uses the decimal, base-10 prefixes, while software always uses the binary, base-2 versions. You’ll find the same issue with the hard drive in your PC or Mac. There has been an attempt to use a different set of prefixes to refer to the binary calculations in order to make it clearer which units are being referred to, but sadly this has not widely caught on.

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