Here's how iCloud works - one device gets a new bit of content, which it then pushed to iCloud and from there it rains down on all your other devices (iPhones, iPads, Macs, even PCs, anything). There's a total of nine apps that work with iCloud to handle the various types of content.
Those apps are: Contacts, Calendar, Mail (the original three from MobileMe), then App Store, iBooks, backup, Documents, Photo Stream and iTunes.
First up is contacts - add or change a contact and iCloud will copy that contact or change to the other devices. Calendar notes are synced the same way and you can share your calendar with other people.
Next up, Mail gives you a free @me.com account and 5GB of free storage. That storage is shared with a couple of other apps. Emails are synced to all devices.
iCloud lets you look at a list of all the apps you've purchased and with a tap of a button, you can download them to the device if it doesn't have it installed already. Buying a new app will push it to all devices, so that's only needed for apps you have right now, before the update.
iBooks has an equivalent function for books. Apps and books can be downloaded to up to 10 devices for free. Everything on the device is backed up daily over Wi-Fi, from settings through photos to application data.
Documents in the Cloud keeps your Pages, Numbers and Keynote documents synced across your devices. Documents and device backups count towards the 5GB storage limit.
Photos also go in the cloud - Photo Stream lets you snap a photo on one device and before you know it, it's already available on your other devices. Photos that come in from Photo Stream have their own album. Photos are synced on your Apple TV as well, which will make showing them completely effort-free.
Note that up to 1000 photos are kept in iCloud and up to 30 days - mobile devices keep that many for that long too, but Macs and PCs keep all photos, always. If you move photos to another album (other than the Photo Stream album) they will be preserved after 30 days too. Photos here don't count towards your 5GB storage limit.
Finally, perhaps the best feature in iCloud - iTunes in the Cloud. If you've purchased a song on another device, tap the cloud button and you can download it on the current device as well. This happens at no extra charge - a first in the industry, Apple says. Newly purchased songs are simply downloaded to all devices automatically.
But it goes beyond keeping your music library synchronized across all the devices. iTunes Match is a great feature if you have a large music library that's not from iTunes. Those songs are scanned and you can listen to high-quality copies of those songs from iTunes (256Kbps AAC, no DRM, same as songs you buy from iTunes). Match isn't free however, it costs $25 a year but that's for 20,000 songs. It's US only too.
Still, the whole scanning process isn't without merit even without Match - iCloud will sync only songs that aren't already on the device, making the whole process much faster (it should be done in minutes, Apple claims).
Now, the whole of iCloud will launch in the fall with iOS5 - but iTunes in the Cloud can be had in beta form sooner, with iOS 4.3 beta.
Those are the 9 core apps of iCloud that Apple provides. But fret not third developers - your apps can also use iCloud to sync their own content across the various devices that have the app. That works for iOS, Mac and PC apps - cool!
Syncing videos is conspicuously missing - the press release says nothing about that and neither did Steve during the presentation.
By the way, the AppStore update is already live, you can now see the full list of apps you've ever downloaded and you can also see the apps you have downloaded on other iOS devices. Go check it out from your device!
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