iCloud is a service that is available on every iOS device running iOS 5 or later. At its most basic level, iCloud is a mechanism for storing files “in the cloud,” i.e. one or many remote servers. iCloud ties the stored data to a particular user in individual iCloud accounts. When you purchase an iOS device, you set that device up with your iCloud account. If you own other devices, you can associate them with your account, too. The shared data in the iCloud is available only to the user logged into the device. If another user logs into the device (which is rare), access to the original user’s iCloud data is removed.

There are two big features of iOS that use iCloud – key-value storage and document storage.