iCloud vs. Wi-Fi Sync: Which does what?

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Thanks to the combination of iTunes 10.5, iOS 5, and iCloud, you can sync data wirelessly with your iOS device. In fact, there are two ways to do so: iCloud syncing, which sends specific information to and from Apple’s iCloud servers over an Internet connection, and Wi-Fi Sync, which syncs your device with iTunes on your Mac via your local wireless network.

But there are notable differences between what gets synced using each method—some things are exclusively iCloud or Wi-Fi Sync, while other things can be synced via either method. And it’s important to note that Wi-Fi sync and iCloud sync aren’t mutually exclusive. You can, and mostly likely will, use both methods depending on the situation and your settings. Which is why it’s easy to get confused about the differences and similarities between the two.

Here’s a quick summary of the types of data handled by each, as well as when each type of data is copied or synced.

Wi-Fi sync

Wi-Fi syncing is identical to tethered (USB) sync—it syncs only data that resides on your Mac. You enable Wi-Fi sync, counterintuitively, by connecting your iOS device to your Mac via Apple’s USB-to-dock-connector cable, and then, in iTunes’s Summary screen for your device, checking the box to Sync With This Device Over Wi-Fi.

Wi-Fi syncing can sync the following types of data between your iOS device and iTunes. Note that, as with USB syncing, Wi-Fi syncing handles only those categories of data you’ve chosen in iTunes to sync to each device.

  • Music, video, apps, books, podcasts, audiobooks, ringtones, and iTunes U content you’ve purchased from Apple and downloaded to iTunes. This includes apps and media you’ve purchased on other iOS devices and downloaded to iTunes via automatic download.
  • Music, video, books, and other media you’ve ripped or otherwise manually added to iTunes.
  • Documents for individual iOS apps that use iTunes’s File Sharing feature.
  • Photos in iPhoto, in Aperture, or in folders on your Mac’s drive that you’ve opted, in iTunes, to sync to your iOS device.
  • Device backups (though only if you’ve opted for local backup instead of iCloud backup).
  • Contacts, calendars, bookmarks, and notes (though only if you’re syncing them locally, via iTunes’s Info screen for your device, rather than via iCloud or MobileMe)

You enable Wi-Fi syncing in iTunes.

Once you’ve enabled Wi-Fi syncing in iTunes, Wi-Fi sync happens automatically, once per day, when your iOS device is connected to power and on the same Wi-Fi network as the computer running iTunes. (If you unplug from power after the sync starts, the sync continues.) You’ll see a sync icon in the iOS device’s status bar during any sync—you can continue to use the device during the sync. You can also force a Wi-Fi sync—with or without power—any time you're on the same Wi-Fi network as your computer and iTunes is running: On your iOS device, go to Settings > General > iTunes Wi-Fi Sync > Sync Now; or on your Mac, select your device in the iTunes sidebar and then click Sync in the lower right corner of the Summary screen.

iCloud sync

Your iOS devices can also sync data wirelessly with iCloud, but iCloud syncing differs from Wi-Fi sync in significant ways. First and foremost, iCloud is the central storehouse of data, rather than your computer—once you've gotten your data into iCloud, your devices sync directly to it. In this way, iCloud is a lot like MobileMe syncing. But whereas MobileMe-to-iOS syncing handled only email accounts, contacts, calendars, bookmarks, and notes, iCloud also handles many of the same other types of data you can sync via iTunes. However, iCloud doesn’t actually sync every type of supported data—for some items, it simply makes media available for you to download.

You choose, in the iCloud screen of the Settings app, which types of data to sync.

The types of data iCloud can sync with your iOS devices include:

  • Contacts, bookmarks, calendars, and notes.
  • Photos you’ve uploaded to iCloud—from your iOS devices, or iPhoto or Aperture on your Mac—using Photo Stream.
  • Device backups—only if you’ve opted for iCloud backup instead of iTunes backup.
  • Documents and data stored in iCloud by iCloud-enabled apps.

There are also types of data iCloud doesn’t sync—it doesn’t upload them to iCloud from your device—but does make available for automatic, over-the-air downloading to your device:

  • Newly purchased music, apps, books, and (for Newsstand publications) periodical subscriptions—only if you’ve opted, in Settings > Store, to automatically download these types of data.

Finally, iCloud makes particular types of data available for manual downloading:

  • Music, apps, books, audiobooks, ringtones, and (in the U.S. and select other countries) TV shows you’ve purchased from Apple.
  • Via iTunes Match (Apple’s $25-per-year music-hosting and -download service), most music you’ve ripped or otherwise manually added via iTunes.

Unlike Wi-Fi syncing, iCloud syncs aren’t all-at-once events—different types of data are synced or downloaded at different times. The following list assumes your iOS device has an Internet connection:

  • Changes to contacts, calendars, and notes are pushed to your iOS device immediately after those changes are made on the iCloud.com website or are received by iCloud from another device.
  • New photos are pushed to your iOS device immediately after they’re added to Photo Stream.
  • Backups occur once a day when your device is connected to power (an AC or DC adapter, a computer’s USB port, or an external battery pack), has an active Wi-Fi connection, and is screen locked.
  • Changes to documents and data hosted by iCloud’s Documents in the Cloud feature are pushed immediately to your iOS device.
  • If you’ve enabled the setting (in Settings > Store) to automatically download music, apps, books, or publications, these items are pushed to your device immediately after they’re purchased on any other iOS device or in iTunes on your Mac. Note that “purchased” includes free downloads from Apple's media and app stores.
  • If you’re an iTunes Match subscriber, tracks and playlists you’ve uploaded to iCloud via iTunes Match are available for streaming playback in the Music app. You can also choose to manually download individual tracks to keep them on your iOS device for offline listening.

As noted above, depending on how you’ve configured iTunes and your iOS devices, you may use iCloud sync only for, say, your photos, documents, contacts, bookmarks, calendars, and notes, but use Wi-Fi sync for music, video, and backups. In fact, movies can be synced only via Wi-Fi from your computer; TV Shows can be downloaded via iCloud in the U.S. and select other countries, but must be synced with your computer elsewhere. And podcasts can’t be downloaded automatically via iCloud—you must manually download them from within the iTunes app or sync them via iTunes on your computer.

Updated 11/16/2011, 11am, to note that over-the-air downloading of TV episodes is also available in select countries outside of the U.S.

Macworld staff editor Serenity Caldwell contributed to this article.

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