As the data files we work and play with keep getting bigger and more numerous, backing them up and moving them to other computers becomes increasingly unwieldy -- a small music collection alone can run into the tens of gigabytes. But the rewriteable CDs most users rely on for these chores hold 700 megabytes of data apiece at most. Even a rewriteable DVD, with roughly seven times that capacity, still can't contain one user's complete personal files.

Iomega hopes to solve this problem with its new Rev drive -- a removable-storage device that can hold 35 gigabytes of data on a removable, $60 cartridge about the size of four floppy disks. It's sold in versions that can be plugged into a PC's internal drive bay ($380) or a computer's USB 2.0 or FireWire ports ($400), with one cartridge included in the box. The internal and USB models require Windows 2000 or XP, while the FireWire model also works in Mac OS X.

Installing the Rev, unfortunately, wasn't as simple as it should have been. Anybody with a CD-RW drive in his PC will need to install updates to whatever third-party CD-burning software he uses before loading Iomega's software and plugging the drive in. But even after heeding this and other warnings in Iomega's documentation, we still didn't avoid all of these "drive letter access" conflicts on several machines.

(You can, however, connect a Rev drive and use it in read-only mode without installing any software.)

Once the drive was properly set up, however, it made regular backups a comfortably simple procedure. Iomega's Automatic Backup Pro program assists users in setting up backup procedures according to a variety of criteria -- you can save your files at scheduled intervals, or every time they're changed. You can even save multiple revisions of the same file, appending a version number to each copy's file name.

It defaults to backing up such standard Windows data directories as the My Documents folder, but if you have files stashed elsewhere, you'll need to tell Iomega's software where to look.

Automatic Backup Pro can also password-protect, encrypt and compress your data -- the last option can fit 90 gigabytes worth of files on one 35-gig Rev, Iomega claims.

We didn't do nearly as well in our tests. Music files, which are generally already compressed, could be squashed only an additional 15 percent or so by Iomega's software, but even Microsoft Office files could be condensed by only 50 percent.

Another application bundled by Iomega, Norton Ghost, will save an "image file" of your entire hard drive -- a complete clone of everything on it. This program had some initial trouble recognizing the Rev drive but worked well afterward. If, however, your hard drive's contents can't fit on one Rev cartridge, Ghost can't span the image file across two cartridges.

Data transfers to the Rev zipped by almost as fast as file copies to external USB hard drives. It opened even the largest files, such as massive video clips, in moments.

An external USB hard drive, however, costs a lot less than a Rev drive -- a 160-gigabyte model from Maxtor with its own automatic-backup software sells for $180. A four-pack of Rev cartridges, at $200, would cost more and store less, and that leaves out the cost of the drive itself.

Hard drives aren't necessarily the most reliable backup media -- but veterans of Iomega's earlier Zip drives, which suffered from a strange flaw dubbed the "click of death," know that any storage device with a lot of moving parts can break down unexpectedly.

On the other hand, the Rev's cartridges, with their small size and light weight, do offer the virtue of being easier to store apart from the computer -- one of the most important aspects of good backup hygiene.

But if your regular backup needs have yet to outstrip the space afforded by one or two CDs or DVDs, stick with those rewriteable discs. They're dirt cheap, they're easy to transport and you can count on reading them on almost any other computer.

Iomega's Rev drive stores data on removable cartridges.