On the Internet, just about everybody's forecast calls for clouds these days. "Cloud computing" is one of those phrases that, in the hands of a marketing pro, can mean anything, but in general it refers to moving your data, your applications or both from an individual computer you can touch with your fingers to a Web-based service you can reach from any other computer online.

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The upsides of cloud computing for you: since the information you want has ascended from your computer's hard drive to an Internet service, you can access it from almost anywhere; collaboration with other people gets a lot easier; your data is automatically and constantly backed up; bug fixes and software upgrades also happen "automagically." And because cloud services can take advantage of far more storage and processing power than a single computer or smart phone can allow, they can enable major advances in everything from voicemail to robots.

The downsides of cloud computing: You'd better have a fast and reliable Internet connection, and the cloud provider had better defend your privacy and avoid endangering your data in a server mishap.


But while Google and Amazon have built portfolios of cloud services and Microsoft has become a recent convert to the concept, Apple has only dabbled in it, fielding such limited offerings as the free iTools and its mediocre, $99/year successor MobileMe. On Monday, though, the Cupertino, Calif., company rebooted its cloud efforts by introducing a new, free service called iCloud — and this time, it says, it's here to stay.

One difference between iCloud and the earlier services of competitors is the company behind it. The company once routinely described as "beleaguered" now attracts an outsized amount of attention; when Apple enters a market, people expect it to upend things. 


Another, more important difference is how your data — contacts and calendars, email, photos, documents and music — can get in and out of iCloud. Apple's built this service as a sort of heavenly hard drive to a designated set of devices, as seen in the company-provided illustration above: your Mac, your PC, your iPhone or iPod touch and your iPad. Most cloud services have far less specific system requirements, usually starting and ending with "any device with a modern Web browser."

Further, iCloud is built to mesh with specific programs. Its Photo Stream connects to an iPhone's Photos app, but not the equivalent software on an Android phone. Its iTunes in the Cloud, unsurprisingly, requires a copy of iTunes. It will let you save a spreadsheet in the cloud and easily edit it from any of your devices–so long as they run Apple's iWork productivity suite.

A third, most important difference: Unlike Google Docs or Amazon's Cloud Player, iCloud doesn't offer Web access to all the content you've uploaded. You can only access it through a dedicated app. That could be a problem, since far more computers have Web browsers than include the specific programs supported by iCloud. In some cases, such as on locked-down machines in offices, you might be allowed to install the required app.

(Update, 6/13, 2:49 p.m. Former Engadget editor Joshua Topolsky got Apple PR to confirm that it will retire all of the current MobileMe Web apps when that service closes on June 30, 2012, without any plans to replace them: “You will no longer be able to log in and check your mail through a browser, change calendar events, or edit contacts.” Update, 6/26, 2:31 p.m. Eleven days after Topolsky's article, Apple posted a Q&A; on the MobileMe-to-iCloud transition that promised Web access to iCloud's e-mail, contacts and calendar services this fall. Left unanswered: How a company that prides itself on elegance as much as Apple does could make such a mess of its message.)


(Disclaimer: I've spoken at a couple of Google-hosted events.)

In fewer words: Where Apple employs the cloud as a cable, other vendors treat it as more of a window. 

By controlling the service and the software, Apple expects to provide the same sort of it-just-works reliability that its control of Mac hardware and the Mac OS X operating system allows on its computers. (Since most of iCloud requires the not-yet-shipped iOS 5 update for Apple's mobile devices, we can only guess if that will work out; keep in mind the ugly debut of MobileMe and subsequent flops by other cloud services.)

Apple's focus on simplicity, however, looks likely to come at the cost of compatibility — just as in such recent proprietary Apple ventures as its iOS- and Mac-only Facetime video-calling system and its just-announced, iOS-only iMessage text-messaging alternative.

If you've already embraced Apple's desktop, laptop and mobile offerings, iCloud could amount to a welcome hug back from Cupertino. But if your computing reality is not so orderly, Apple's cloud may seem more like a curtain.