Introduction to the Cloud - Beginning iOS Cloud and Database Development - page 16

Figure 2-2. iCloud reads the Ubiquity Container to check for changes
Designing for iCloud
This efficient process of only sending chunks of data keeps us from having to send megabytes
or even gigabytes of data back and forth to iCloud. In addition to these chunks, files in your
applications also have a lot of associated information, such as name, modification date, size, file
type, and so on. This metadata is pushed to iCloud as well.
Most apps also aggressively push all this metadata to iCloud, so that even before a file is finished
uploading, the name, modification date, and so on, are identifiable in iCloud. This makes for a better
user experience, because even though the file may not be opened immediately, it will still show the
data as a placeholder on the screen.
iOS and Mac OS iCloud
There is a significant difference between how OS X and iOS handle file downloads. Any files that are
stored on OS X are downloaded aggressively from the iCloud to the Mac. This is because iCloud
knows that a Mac has more storage capacity than your iOS device. With iOS devices, applications
know all the files that are available in iCloud, but the application will only ask for specific files to be
brought down to the device. This saves a significant amount of storage on the device and allows for
faster download speeds.