Since we’re not getting Mac OS X 10.5 “Leopard” and its automatic backup feature “Time Machine” until October, I thought this would be a good time to tell you about a shareware backup utility called SuperDuper!

About six months ago, with the idea of having one network-accessible drive to which I could back up all of my Macs, I bought a 500-gigabyte Buffalo LinkStation for much less than I paid for my very first hard drive (a 40-megabyte wonder circa 1990).

So I had plenty of space, and plugging the LinkStation into my wireless router made it available to both my G4 Mac tower and my MacBook. But which backup utility to use?

I prefer to create complete backups of my hard drives that include every file. In the event that a primary drive goes south, I want to be able to restore it EXACTLY as it was, right down to location of the Desktop icons. I also want the ability to retrieve an individual file easily, should the need arise.

Because of a component of Mac OS X’s Unix underpinnings called permissions, copying files the plain old Mac OS 9 way doesn’t work if you like full, bootable backups. How each backup utility handles this issue is critical. Several of those I tested, such as Apple’s own imaginatively named Backup, worked around the permissions problem by backing up mainly data such music, documents, videos and the like, as well as certain preference files. But that won’t give you a full, bootable backup.

SuperDuper!, created by a tiny software company called Shirt Pocket, came up with what I consider a great solution to the permissions issue in a feature-rich, easy-to-use and reasonably priced ($28) package.

The SuperDuper! answer to the permissions problem is a common Mac OS X sight: disk images. Disk images are commonplace in Mac OS X; many software files Mac users download arrive as disk images, which appear at first to be a single file. When you double click on it, a second icon appears on the Desktop, which behaves as though it were a hard drive or removable media such as a USB flash drive.

This turns out to be a great way to generate and maintain backups of hard drives, particularly because SuperDuper! uses a special kind of disk image called a sparse image. Usually a disk image is a fixed size; once created, it can’t be enlarged to hold more data. But like a balloon, sparse disk images consume only as much space as the data they contain. So when you add more data, the sparse disk image grows to accommodate it – perfect for maintaining a backup of an ever-filling hard drive.

Should you need to access a file on the backup, all you need do is double-click on the disk image, and a mirror of your Mac’s hard drive as it was when you last ran SuperDuper! appears on your Desktop.

Like many good backup utilities, SuperDuper! offers a “smart update” option to ensure that your existing backup image matches what’s on your hard drive. The process is much faster than generating the entire backup from scratch. The software checks both the Mac hard drive and the backup disk image, copying new files to the image while updating or deleting those that the user has changed since the last backup. Of course, you still need a backup storage drive large enough to handle your ballooning sparse disk images. But external hard drives with 500 GB of storage can be had for under $300; those with 300-400 GB have dropped under $200.

Other things I liked about SuperDuper!:

Universal Binary: It runs on both the older Power PC-based Macs as well as the newer Intel-based Macs.

Informative interface: When SuperDuper! is doing its thing, it conveys its progress with constantly updated statistics on files checked, files copied and files deleted. For the hopelessly geeky, it even tells you how fast it’s copying in megabytes per second.

Network-friendly: SuperDuper! doesn’t care where your backup disk is – it can be internal, USB external, FireWire external or on a network -- so I can back up my MacBook wirelessly to the LinkStation. Most excellent.

Scheduler: Though common to any quality backup utility, SuperDuper! provides a very clean, straightforward way to schedule automatic backups.

Of the half-dozen or so OS X backup utilities I tested, none had the combination of features, efficient operation, and low cost of SuperDuper! You can download a free trial from the company’s Web site; it’s functional, but disables some of the really useful features such as Smart Update.