When I heard that iCloud (free to $100 per year; $24.99 for iTunes Match), Apple's free data-syncing service, supported Windows machines, I was at first slack-jawed—and in a good way. Was it true? Could Mac users now access their Calendar, Contacts, iTunes music, photos, and other files from a PC? My open mouth tightened to a mere smile when I realized the answer was, "Well, sort of."

iCloud inhabits several Apple services, including the iOS, Mac OS, iTunes, and the Web. This can make it difficult to wrap your head around. Despite this, iCloud is an excellent service, providing automatic backups of iOS devices and syncing for photos, music, Calendar, Contacts, and some document types. But don't confuse it with other file-syncing services along the lines of SugarSync (4.5 stars) and Dropbox (4 stars). Those two services, both PCMag Editors' Choice products, as well as Microsoft SkyDrive, give you access to any files you mark to be synchronized from virtually any machine. For example, you can create and save a presentation on your office computer, sync it, and then access it from your home computer or mobile device by simply logging into the service.

Apple's iCloud does synchronize some document files, but not any old thing you want. iCloud doesn't think about syncing documents per se. It thinks about syncing the data you have associated with an app. For example, iCloud can synchronize office files made with Apple productivity software iWork and let you access them anywhere an iWork app is installed. And this is the only real way that iCloud under Windows suffers, since you won't be running iWork in that OS any time soon.

iCloud also syncs images across your iPhone, iPad, Mac, and even a Windows PC. iCloud makes music you buy through iTunes accessible to you from any instance of iTunes. With the optional add-on service iTunes Match ($24.99 per year), it will sync and store up to 25,000 music files (no matter how you got them) that you have in your iTunes library. But iCloud doesn't synchronize many other files that you create or edit in other apps.

Once you understand what iCloud can and can't do, you'll likely find that it's a valuable and worthwhile service nevertheless, but that doesn't mean you don't also need another file-syncing service. All Apple device owners should sign up for iCloud as soon as humanly possible, but know that it won't meet all your file-syncing needs.

iCloud Sign Up and Requirements

To get iCloud, you need an Apple ID plus at least one of the following devices:

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• Mobile device running iOS5 (iPhone 3GS, iPhone 4, iPhone 4S, iPad, iPad 2, iPod touch 3rd or 4th generation; see How to Get Apple's iOS 5 for help)
• Mac computer running OS X Lion 10.7.2
• A Windows PC running Windows 7 or Vista SP2.

From a Mac running Lion, look under Preferences for the iCloud logo. Select it to dig into the options. On a Windows desktop or laptop, you'll want to surf over to apple.com/icloud/setup to download and install the local software. Additionally, there is a Web interface at iCloud.com where you can access some of your backed up information online, but it's not a very comprehensive system (more on that later).

For iPhones and iPads, look in Settings for the new iCloud icon that will appear after you update to iOS 5.

Tips for Backing Up Your iPhone and iPad

One part of iCloud that you should definitely take advantage of is automatic backup. From the iCloud page of the Settings panel, look toward the very bottom of the screen for the option Storage and Backup. Make sure "iCloud Backup" is switched on. Then, you'll want to poke around in the Manage Storage section, especially if you have a lot of apps, to further determine what should get backed up and what doesn't need to be. By turning off apps that are not important, you can save a lot of space. If saving space isn't your thing, you could just buy more space. Apple gives iCloud users 5GB to start, but you can buy up to 50GB more (making 55GB total) for $100 per year. iOS devices only back up over Wi-Fi so there's no worry about the service hogging data from your data plan.

A second feature to jump on upon installing iCloud is Find My iPhone or Find My iPad. Turn it on, and it can help you locate or remotely wipe a lost or stolen phone or tablet. There's also a Find My iPhone/iPad app, which you can use to locate lost devices, including Macs, provided you set up Find My Mac on your laptop or desktop.