Backup 3.1, which is free for members of Apple's $99-per-year MobileMe (formerly .Mac) service, has some useful features and a reasonable interface. It creates additive incremental archives (though not duplicates) onto hard disks, network servers, optical media, or your iDisk. As of publication time, it hasn't been updated since the release of Time Machine, and I don't know if Apple has any plans for its future development. But because it lets you easily back up small chunks of data to a variety of media, it's actually more flexible in some respects than Time Machine.

One issue is that it backs up only files belonging to the currently logged-in user. If you're the only person using a machine, that's no big deal. But if two or more users share a Mac, each one must log in and run Backup separately to back up that user's files. Virtually all other backup programs can handle data for multiple users at once.

The first application designed exclusively for creating bootable duplicates under Mac OS X, Carbon Copy Cloner (available from http://www.bombich.com/software/ccc.html) has evolved into a powerful yet friendly tool. And the price is right (free; donations suggested.) Version 3.1 of Carbon Copy Cloner correctly copies every last kind of obscure metadata I throw at it, something only a couple of other programs can do. That gives me warm fuzzy feelings.

One unusual capability is that Carbon Copy Cloner can create a bootable duplicate onto a network volume shared by another Mac (as long as you can get administrator access to that volume, in order to install a special program that Carbon Copy Cloner relies on). That doesn't mean you can boot over the network, but it does mean that you can restore a duplicate over the network and then boot from it, or directly connect the target drive to your Mac via FireWire (or USB, for Intel-based Macs) to boot from it. The only other Mac backup program I know of that can currently pull off this trick is Retrospect.

Code 42 Software's CrashPlan (http://crashplan.com) is an unusual, category-defying product with most of the features of a good archiving program, online storage capabilities, and the unique option to perform peer-to-peer backups—locally or remotely. It's a refreshingly different way of thinking about backups.

The key component of CrashPlan is its eponymous software, which can create archives (but not duplicates) on any of these destinations:

(Absent from this list is an external hard drive; currently, you can't designate a volume mounted on your computer as a backup destination for your own files, but Code 42 says this feature is on its way.)

CrashPlan supports block-level incremental archives and avoids storing any duplicated data—even if two identical files came from different computers—in order to save space. (The $19.99 basic edition of CrashPlan stores just the most recent version of each file, while the $59.99 CrashPlan Pro creates true additive incremental archives, with as many old versions as you want. You can save money on CrashPlan with the coupon at the end of this book.) And, rather than running backups on a fixed schedule, CrashPlan Pro can dynamically watch your computer as you work, backing up any new or changed files right away (or after a user-defined delay). This means that backups, after the first one, appear to take no time at all; they simply happen automatically in the background as needed.

In almost every case, CrashPlan simply does the right thing without presenting lots of confusing options. Backups are always compressed and always encrypted, so you need not worry about your friend being able to read the data you've backed up to his computer. Files you've modified more recently are backed up first, so that even if you're waiting days for an initial full backup over the Internet to finish, the files likely to be most important to you are protected; it even backs up multiple versions of files you modify while that backup is in progress. You can specify files, folders, or extensions to exclude, set times when CrashPlan won't run at all, and throttle its bandwidth use if need be.

I've been a fan of Prosoft's Data Backup for some time, and with version 3 it's gotten even better. It has a thorough, solid feature set, competently creating both archives (optionally with compression and/or encryption) and duplicates. It can wake up your Mac to perform scheduled backups, which can run even if no one is logged in. And yet it features a straightforward, uncomplicated user interface. It's not even expensive ($59, and you can save money with the coupon at the end of this book). Learn more about Data Backup at http://www.prosofteng.com/products/data_backup.php.

Two other applications I can think of (Personal Backup X5 and Tri-Backup—interestingly, both made by French developers) have feature sets that are similar, overall, to Data Backup's, and are around the same price. I happen to prefer Data Backup's look and feel, and have found Prosoft to be a responsive and helpful developer, but you should have satisfactory results with any of these three.

Amazon.com's S3 (Simple Storage Service) provides inexpensive, secure file storage on Amazon.com's servers. To sign up for Amazon S3, simply fill out a form (including credit card information) at http://www.amazon.com/s3. After your account is activated, Amazon.com provides you with two long strings of characters—an Access Key ID and a Secret Access Key—both of which you'll need to reach your space on their servers.

To get at your S3 storage space to do useful things like uploading or downloading files, though, you'll need some sort of third-party software. At the moment, the best tool for this job is a $20 program called JungleDisk (http://www.jungledisk.com).

JungleDisk can perform some behind-the-scenes magic to mount your S3 storage space as a network volume. With the JungleDiskMonitor application running and your S3 storage space mounted in this way, most backup programs can access your S3 storage space.

However, you may not need another program at all, because JungleDisk is quite capable in its own right. It supports additive incremental archives and rotating archives, with rather detailed control over if, when, and how older files are purged from your archive to save space.

With optional JungleDisk Plus service for $1 per month, JungleDisk gains the capability to perform block-level incremental updates, saving considerable storage space. JungleDisk Plus also lets you access your S3 files via a Web browser, resume interrupted uploads, and more. If you decide to use JungleDisk, this extra service is a no-brainer in my opinion, because you'll likely save more than $1 per month in storage fees paid to Amazon.com.

A relatively new backup tool called QRecall is worth considering. Like CrashPlan (and unlike Time Machine), it can save space by eliminating duplicate copies of identical files from more than one computer. Also like CrashPlan, it offers compression and block-level incremental updates, so that large files need not be entirely duplicated every time they change.

QRecall works with external hard drives and network volumes, and has a long list of clever, useful features. However, it does not currently support encryption or optical media, can't make bootable duplicates, and has a peculiar interface that introduces several unusual terms (such as "capture," "recall," "layer," and "timeline") that force you to think about backups in ways you may not be accustomed to. Each license (for either a single user or a household) costs $40, though as I write this an introductory price of $30 is in effect. Get QRecall at http://www.qrecall.com.

EMC's $129 Retrospect Desktop used to be my favorite backup program. It's still peerless in terms of raw features—it does tricks no other Mac backup software can do, and its support for client-server network backups is exceptional. But its performance is substandard; it has some significant bugs; it hasn't yet been updated to be a universal binary, which would run natively on Intel-based Macs; and it has a user interface only a mother could love (with a steep learning curve to match). In addition, EMC is sometimes slow to add support for newer storage devices; if you buy the latest and greatest optical drive, you may have to wait several months before an update includes the necessary driver. (FireWire hard drives are always supported automatically.) Happily, EMC is planning a major update—Retrospect X—for release in late 2008 that will, I hope, address many or all of these concerns.

Even in its current version, Retrospect is the best choice for making incremental backups to recordable DVDs, because it's the only Mac backup program that can record multiple sessions on a single disc—others make you pop in a new, blank disc every time they run, even if the last one had only a tiny amount of data on it. Retrospect also has great flexibility in selecting files to include or exclude and scheduling backups, and offers excellent compression and encryption. Also, Retrospect Desktop supports most MO (magneto-optical) and tape drives (http://www.emcinsignia.com/products/smb/retroformac).

If you already own a copy of Retrospect and it's working well for you, by all means feel free to continue using it. If you want to use Retrospect but find it confusing, see the Online Appendixes, in which I offer advice to ease your initial configuration. But unless you need one of Retrospect's unique features, I suggest that you use another backup application—at least until Retrospect X appears.

If you're looking for backup software to make bootable duplicates, SuperDuper is a fantastic choice—it's exceptionally easy to use, with a simple user interface and plain-English descriptions of exactly what will happen. The software costs only $28, and you can download a free version that will create a bootable duplicate but which lacks the capability to update it incrementally.

In my testing with version 2.5, SuperDuper failed to copy a couple of relatively insignificant kinds of metadata, whereas Carbon Copy Cloner handled them perfectly. Apart from that one tiny complaint, I can't come up with anything bad to say about SuperDuper, and it's the program I use most often when making duplicates of my own disks (http://www.shirt-pocket.com).

Time Machine, which I describe in detail later, in Configure and Use Time Machine, is the slick backup program Apple built into Leopard. It's the easiest way, by far, to create and restore archives—and it's what I recommend for most people running Leopard. However, you may not be most people. So I want to look at a few situations in which it may be the wrong solution—and what to do instead.

Without a doubt, Apple got a lot of things right about Time Machine. It also has some bugs—see Avoid (or Solve) Time Machine Problems—some of which may be remedied by a free update to Mac OS X. Beyond these minor problems, however, are larger design decisions that are unlikely to change anytime soon. If the fundamental design of Time Machine is incompatible with your needs, then you should choose a different solution for archiving.

Time Machine makes a poor match for these backup needs: