The order is said to coincide with the forthcoming release of a new product that Isilon is expected to announce next week.

So huge an order for data storage would coincide with the construction of Apple’s huge data center in Maiden, N.C., and that’s expected to be the hub for a new version of iTunes that relies more on storing media in the cloud and less on using its customers local hard drives.

If you have trouble getting your head around the petabyte, the fine folks at another EMC unit, the backup service Mozy (soon to be a unit of VMWare) produced this fascinating graphic. As they tell it, one petabyte is enough to store more than 13.3 years worth of HD video, meaning 12 petabytes would be enough to store nearly 160 years worth.

The scale of the storage infrastructure, if true, would amount to another potentially intriguing clue to the environment Apple is using inside its data center. Previously it had disclosed in job ads on its Web site that its hardware there will include a mix of systems running Mac OS X, IBM’s AIX, Oracle’s Sun/Solaris, and some Red Hat Linux-based machines.

PREVIOUSLY:

• Apple’s Area 51: The Truth Is Out There
• Apple’s N.C. Data Center Intended for iTunes, MobileMe
• Apple Owns Another 70 Acres Near NC Data Center
• Was Apple Planning on Doubling Its North Carolina Data Center All Along?
• Apple Reaching for the Cloud With MacBook Air and N.C. Data Center
• That’s Apple’s New Data Center? Where’s the Giant Glass Cube?

A: The built-in backup program in your iMacs, called Time Machine, doesn’t require Apple’s Time Capsule product to work. It will work with almost any brand of directly connected external hard disk.

For instance, I back up my home iMac to a Western Digital drive that’s connected to it via a cable.

As for hard-drive life, it’s my experience that many seem to die sooner or later, especially if they are used heavily. I don’t know if the ones inside the Time Capsule are especially fragile. But, in just the past six months, I’ve had an external hard disk from G-Tech die on me; seen an internal hard disk on my home Dell die for a second time; and discovered that the hard disk on my colleague’s MacBook died.

One way to protect against the failure of a local backup drive is to consider, in addition to using an external disk, backing up your data to an online backup service like Mozy, Carbonite or SugarSync.

My Dell has Microsoft Vista but I can upgrade free to the new Windows 7. However, I was told my antivirus software won’t be compatible and my email will change—the program will no longer be “Windows Mail.” What do you recommend?

A: I regard Windows 7 as much better than Vista, but you are correct that many antivirus programs will require upgrading and Windows Mail will go away during the upgrade. You’ll have to install a new email program, such as the very similar “Windows Live Mail,” which can import your messages. So, the question really is one of trade-offs. If you’re satisfied with Vista, and would rather not perform these program replacements, you should stand pat. If you don’t like Vista, and are anxious to replace it, then the hassles you describe could be worth it.

Will Office 2003 work with the new Windows 7 operating system?

A: Microsoft, which makes both products, says the answer is yes, though I haven’t tested it.

Is it possible that the Verizon Motorola Droid, which doesn’t work in Europe, could be turned into a “world phone” that could work on European cellphone networks via an app somebody might develop?

A: An app wouldn’t be able to do that for the current Verizon Droid. It’s a hardware issue.

Verizon’s Droid, like most Verizon phones, is built to run on a type of network called CDMA that isn’t used in Europe or most other countries outside the U.S., which use a network standard called GSM.

To run on these networks, the Droid, or any other current CDMA phone, would need an entirely different radio, or two radios, one for each type of network.

Verizon offers a handful of so-called “world phones,” which have both kinds of radios inside, but the Droid isn’t one of them. Motorola may well make a new model with two radios, or even a model with one radio that would work overseas, and I wouldn’t be surprised if it did so.

What could be done with an app is to allow the Droid to make so-called VOIP phone calls via the Internet.

In fact, while I haven’t checked, there may already be such an app for Android—the Droid’s operating system—that would do so. But, in many cases, making such Internet phone calls requires the user to be in range of a Wi-Fi network. Some carriers don’t allow such calls to be made over their cellular networks.

You can find Mossberg’s Mailbox, and my other columns, online for free at the All Things Digital Web site, http://walt.allthingsd.com.

Does the new Palm Pre smart phone use the traditional Palm operating system and the many programs that have been written for it?

Palm’s Pre, which is due out later this year to compete with the iPhone and the BlackBerry, doesn’t use this older software, which was once the best smart-phone operating system, but has grown stale. It uses an entirely new operating system called the Palm webOS, which will have to attract developers willing to write new programs for it. It is a clean break from Palm’s previous hardware and software.

How does the Clickfree computer backup system you covered last week compare with Apple’s Time Machine or online backup services like Mozy or Carbonite?

Clickfree simplifies the chore of backing up files to an external hard disk. However, as I noted in the review, it doesn’t back up your whole hard disk, it doesn’t work automatically in the background, and it doesn’t create a backup physically distant from your computer.

Time Machine, which is built into the Macintosh operating system, automatically backs up your entire computer in the background and includes a very easy method for recovering files. It works with external hard disks. But it doesn’t work on Windows PCs, and it doesn’t create a remote backup over the Internet.

Mozy and Carbonite are online backup solutions. Their advantages are that they work unattended and create offsite backups. But they aren’t intended to back up an entire computer, they don’t create a local backup, and they carry service fees.

Does my 13-inch MacBook come with the capability to view PowerPoint files?

No. While Macs come out of the box with the ability to view and create files in the Microsoft Word and Adobe PDF formats, they don’t come with a PowerPoint viewer. In order to view (and create) PowerPoint files on a Mac, your best bet is to buy the Macintosh version of Microsoft Office, which includes PowerPoint itself. There are other methods as well. For instance, Apple’s own lower-priced iWork suite can also open PowerPoint files and create files in the PowerPoint format. And some Web-based office programs, like Google Docs, allow you to view PowerPoint files on Macs.

You can find Mossberg’s Mailbox, and my other columns, online free of charge at the new All Things Digital Web site, http://walt.allthingsd.com.

I can’t figure out how to remove a song from my iPhone. How do I do it?

Unlike an iPod, the iPhone has no purely manual-mode option, which would allow you to drag songs on and off of it. However, there are alternative methods.

The simplest approach is to connect your iPhone to your Windows PC or Mac, and allow it to synchronize as usual. Then, select your iPhone in the list at the left edge of the iTunes window in order to bring up the iPhone-settings functions in the large window at the right in iTunes. Click on the Summary tab, and check the option called “Only sync checked items.” This will limit the songs and videos the computer places on the iPhone to those for which you have checked the little box that appears next to their names in iTunes. Next, go into your music library, or into any playlists you have selected for syncing with the phone, and uncheck any songs you no longer want on your iPhone. The next time you perform a sync, these songs will be removed from the phone.

Another method is to place all the songs you want on the iPhone into a single specially designed playlist, or several such playlists. Then, go to the Music tab in the iTunes settings screen and click on “Selected Playlists.” Next, check off only your special iPhone-bound playlists. Once this is done, you can control which songs are, or aren’t, synchronized to the iPhone by adding or removing songs from these playlists. If you remove a song from one of these playlists, it will be deleted from the iPhone the next time you perform a sync.

Neither of these methods will delete the songs from your computer or your iTunes library, or prevent them from playing on your computer.

I have tried to download some pictures recently and use them as wallpaper. I am storing them in my My Pictures folder. But, when I choose to make them my wallpaper, they appear multiple times on my desktop. How can I have a picture cover the whole background on my monitor?

Assuming you are using Windows XP, go to the Display control panel and select Desktop, then find the image in the Background list and select it. Then, under Position on the right, select Center or Stretch. Note, however, that if you have downloaded a small image from the Web, and your monitor has a relatively high resolution, the Center option won’t allow the image to fill much of the screen. The Stretch option, while filling the screen, may result in a grainy and/or distorted image.

I was wondering if you could recommend a good service for automated online backup of a PC running Vista. All the services I have found require the user to manually transfer files to the online site. In my ideal world, I could set up my machine to transfer the files during the evening.

There are two automated online backup services I’ve tested and reviewed, Mozy (mozy.com) and Carbonite (carbonite.com).

Both work on Vista, neither requires manual file transfers, and both are good, though I preferred Mozy when I last tried them in December 2006. However, Carbonite has released a new version I haven’t tried yet, and Mozy has also been updated since then. I don’t think you’d go wrong with either. You can read my review at ptech.allthingsd.com/20061214.

Mozy offers two gigabytes of backups free, and charges $4.95 a month for unlimited backup, though you can save by paying one year or two years in advance. Carbonite offers a 15-day free trial, after which you pay $50 a year for unlimited backup, though you can save if you pay upfront for two years.

You can find Mossberg’s Mailbox and my other columns online free at the All Things Digital Web site, http://walt.allthingsd.com.

Write to Walter S. Mossberg at mossberg@wsj.com

You could, of course, automatically back up your files to an external hard disk, attached to your PC or to your home network. But that can get expensive, and it doesn’t store your backup remotely, so any disaster at your home or office could also wipe out your backup drive.

There’s another method: backing up over the Internet to a remote server somewhere. This is automated and solves the location issue, but in too many cases it has been costly and complicated, usually with quotas on how much you can back up.

Now, things are changing. I have been testing two online backup services that offer unlimited capacity — no quotas or limits at all — for around $50 a year.

One, called Carbonite, has been unlimited from the start, and Mozy, which previously had limits, is offering unlimited capacity as of today.

Mozy and Carbonite can be set to back up only a few key folders or types of files — say, all your work documents or music files — or, you can set them to back up nearly everything on your computer. If you have a loss, whether a single file, a folder, or everything, they allow you to recover it. Also, you can back up multiple computers with Mozy and Carbonite, but you have to pay extra for each additional machine.

The two services are easy to set up and easy to use. Each worked fine in my tests, both for backing up my key files and also for restoring them.

Carbonite can be downloaded at www.carbonite.com or purchased in stores. There is a 15-day free trial, after which it costs $50 a year, though some stores also sell a $15 version that lasts for three months. The trial version doesn’t back up music or videos by default.

Mozy can be downloaded from www.mozy.com and costs $4.95 a month, or $54.45 if you pay for a year in advance. Mozy also has a totally free version, which is limited to two gigabytes of data. (That is likely to be more than enough, by the way, to cover all of a typical consumer’s word processing, tax and budget files, and plenty of photos.)

Both services currently run only on Windows XP, but both expect to work on the new Windows Vista operating system. And both companies plan to release Macintosh versions next year.

Each installs a fairly small program on your PC that constantly works in the background to back up your data. When a file changes, or a new file is added, it is queued for backup. Carbonite backs up new or changed files 10 minutes after you save and close them, but only backs up each file once a day. Mozy checks the hard disk every two hours and backs up everything that is new or changed. With Mozy, but not with Carbonite, you can also opt for a scheduled backup at a time and interval of your choosing.

The biggest drawbacks of these two products are that backups can be very slow, especially the first backup, and you must have Internet access to do backups and to restore your files. In my tests, on a very fast Internet connection, it still took many hours to do a fairly small initial backup with each product, consisting of about five gigabytes in one case and under two gigabytes in another. A larger backup could take days, though subsequent backups would be much, much quicker.

Both companies encrypt the backed-up files and say they don’t view them. Both try to avoid overburdening or slowing down your computer and Internet connection by going idle or slowing down when you are using your computer for other tasks.

To restore files with Carbonite, you open a sort of virtual representation of your backed-up files and click on what you want restored. If your computer is stolen or not functioning, you can also go to a Web site to initiate a full restore to a new computer.

With Mozy, you can also restore files and folders via a virtual view of your backup that resides on your PC. But Mozy has a much richer Web interface for viewing your backup and for restoring files. From a Web site on any PC, you can log into Mozy and pick any file or folder to retrieve. I even logged in from a Mac, opened a Mozy backup of my Windows PC, and recovered a photo that was then downloaded to the Mac.

Of the two products, I prefer Mozy. Carbonite is a little quicker and simpler to set up, but it’s more limited. If you want to go beyond the default backup choice — your most common documents and settings — you have to troll through your hard disk to select additional folders and files for backup. Mozy also has a default setting, but makes it much easier to alter or customize it.

Mozy offers more-versatile restoring and scheduled backups, and unlike Carbonite, will back up an external hard disk. Mozy will also send you a DVD of all your files, for a fee. Carbonite won’t. Mozy also keeps multiple versions of any file for 30 days. Carbonite doesn’t.

Still, you won’t go wrong with either of these two services, and you’ll sleep better at night.

Email me at mossberg@wsj.com.