How large is iOS?
Solution 1:
The exact answer will vary by device, because there are separate iOS builds for each one. The easiest way to figure this out is to examine an iOS 6 install image (a .ipsw file).
The iPad 3 (Wi-Fi only) is the iOS device that is most similar to a Microsoft Surface, although the two are still very different. The iOS 6.0 (build 10A403) install image weighs in at around 1.15 GB.
The IPSW file itself is actually a zip file that contains several files, but most of them are fairly small. The root filesystem disk image, which contains the entire installed OS, weighs in at around 1.12 GB in this case.
Someone with a jailbroken device could decrypt the image and provide a more exact answer, that's a pretty good estimate of the amount of space it will consume on the device when installed.
Solution 2:
A quick survey of friends a while back has shown that you can expect the following amounts of usable space on an iPhone 5 with iOS 6:
- 13.70 GB of space on the 16 GB model
- 28.00 GB of space on the 32 GB model
- 57.20 GB of space on the 64 GB model
The builds for iPad and iPod touch are different than each iPhone build, but the space taken by iOS when installed and overhead is in the 2.5 GB range across devices and storage configurations. The upgrade to iOS 7 left 27.94 GB of capacity according to iTunes when the device is connected.
The same iPhone 5 on iOS 8:
- ?? GB of space on the 16 GB model
- 27.35 GB of space on the 32 GB model
- ?? GB of space on the 64 GB model
Solution 3:
The iOS 6 .ipsw file, used to restore it, is around 1GB, depending of the device. When installing through the iPhone itself, though, it asks for at least 2 GB of space.
It's fair to presume, then, that the required space is between 1 and 2 GB.