My twins love cd-roms but don’t know how to take care of them. They destroyed their prized copies of Dr. Seuss’s ABCs and Arthur’s Birthday, two discs that Broderbund’s wizards made back in the 1990s. I tried polishing the CDs and largely failed. So I threw them away and burned myself new ones.

Copying CDs is an activity that most people associate with illegal music distribution and downloading. But there’s nothing wrong, morally or even legally, with making backup copies of my own CD-ROMs for my own use – provided that I don’t start sharing those backups with all of my friends.

The easiest way to back up a CD or CD-ROM is to copy its contents onto a recordable CD (CD-R). The danger with this approach is that CD-Rs are more fragile than commercial CD-ROMs: many have thinner-than-paper labels that are easily damaged, especially by little hands. Moreover, most CD-Rs are not archival, meaning that they can lose data as they age and deteriorate. But the biggest danger with archiving a CD on a CD-R is that it is simply too tempting to use the backup when the original dies – rather than making a copy of the copy.

Instead, I prefer to “rip” the CD-ROM, making a byte-for-byte copy of the entire disc on a 200-gigabyte hard drive that I keep specifically for this purpose. There are several disk-imaging tools available to do the copying; on my Mac, I use Apple’s own Disk Utility, while on Windows, I use WinImage 6.1. These programs create a single file that’s several hundred megabytes long. When the CD-ROM is inevitably damaged, I burn the image onto a fresh CD-R.

Computer hard drives die as well, of course. In the old days the standard way to back up a disk drive was onto magnetic tape. These days if you’re storing less than a few terabytes, it’s cheaper per gigabyte to buy external hard drives with USB or Firewire interfaces than to buy high-capacity magnetic tapes and drives. Although tape should be cheaper, disk drives have economies of scale in their favor. So I actually have two 200-gigabyte hard drives; each backs up the other.

Children’s CDs are just a few of the CD-ROM images that I have sitting on these drives. I also image practically every piece of commercial software that I buy, as well as those “installers” that I download when I purchase software over the Internet. That way I can uninstall and reinstall the software if something goes wrong – or when I buy a new computer system. (It’s also important to save the corresponding activation codes.)

One of the problems that I’ve noticed with children’s old CD-ROMs is that many of them won’t run under Windows XP, Mac OS 10.3, or other modern operating systems. So in addition to archiving the CD-ROMs themselves, I’ve also taken to archiving all of my old Microsoft and Apple operating systems. When the hard drive on the kids’ computer died last year, I reinstalled a copy of Windows 98, and they were up and running by the end of the weekend.

Backups are a problem for information stored not just on CD-ROMs but also on computer hard drives. Back in the bad old days of computing – say, ten years ago – most small-business users and many home computer owners religiously made backups of their data. But in recent years, hard drives have become so reliable that many people have simply stopped making backups. Alas, living without backups is living dangerously, as there are many potential ways to lose your data: fire, flood, thieves, software crashes, errant spyware – and, of course, the biggest threat of all: human error.

Now that we are all living in the 21st century, backing up computers is a chore that no one should be forced to remember. I’ve taken care of this by programming all of my computers to back themselves up automatically. A script that runs every night copies the contents of my documents directory to a different Zip file on that same oversized external hard drive. This backup proved to be invaluable this past summer, when my computer crashed while I was running Quicken, and the program’s database was corrupted. And my Zip archives, in turn, are automatically copied from my home computer to a computer sitting under my desk at MIT – just in case my home and its contents are suddenly wiped out.

A few years ago I designed a peer-to-peer backup system based on this concept. The idea was to let businesses back up their servers, desktops, and laptops onto the spare disk space scattered throughout their offices. The network would automatically keep track of what had been backed up and where – and, of course, everything backed up would be encrypted to prevent accidental data compromises. Home users could arrange for backups between their desktops and laptops or, even better, could back up their systems to those of their friends next door.

Unfortunately, I couldn’t find anybody to fund my idea. Nevertheless, many similar systems are now under development. Within a few years, it’s likely that we’ll all be using disk images and peer-to-peer backups to archive our most important information – and probably everything else, as well.