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Apple notes:

1GB = 1 billion bytes; actual formatted capacity less.
1GB = 1 billion bytes; actual formatted capacity less.

Why is the actual formatted capacity less than the unformatted capacity?

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Where did you read this? Bease until recently Apple displayed the size of a disk in Base 10 insted of Base 2 ( or perhaps it was the other way ) in either direction only recently was an option added to OS X to display either. Windows has always used based 2. –  Ramhound May 14 at 11:49
    
@Ramhound edited. tech specs of iPod, iPhone, iPad, etc –  nicael May 14 at 12:15
    
Right. So free space on iOS devices are reported in base 10, the file system and operating system take up some of that space, and the size of the operating system isn't reported on iOS devices. ( at least not by the device itself ). –  Ramhound May 14 at 12:49
    
    
@EnmosProje No. –  nicael Jun 26 at 10:13

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+50

Formatting here really means partitioning and creating file system(s).

Depending on the file system used, a more or less extended part of the media will be used to store non data stuff.

This includes tables used to identify used and unused areas, the file system hierarchy, journals, file metadata (owner, permissions, timestamps, acls), checksums, etc. Some space is also lost due the record size used (a one byte file will use more than one byte on disk).

Not to mention the confusion created by the normalization of the GB unit, which used to mean 1073741824 bytes (i.e. 1024x1024x1024 = 2^30) for decades but now should (rightly) mean 1000000000 bytes (i.e. 1000x1000x1000).

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OS X and Windows also displayed the size of the disk in an entirely different base. One was base 2 the other base 10 until recently. HDDs are sold on the base 10 number by the way. –  Ramhound May 14 at 11:51
    
You also have to take into account the device's operating system which probably takes a couple hunderds of MB. –  Kwaio May 14 at 12:33
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A binary gigabyte is now known as a gibibyte (GiB). –  Cees Timmerman May 14 at 15:15
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@jilliagre I was speaking for the ipod specific case. it is delivered with a X GB drive, but OS takes a part of it. –  Kwaio May 14 at 15:52
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The use of GB to mean a base 2 GiB is not unusual even today, and frankly in electronics and software engineering the base 2 version is a much more useful unit as 1000000000 bytes is a meaningless quantity in nearly every context in technology. –  Vality May 14 at 16:07

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