I often rail on and on about backing up your computer — and for good reason — but it’s about time I explained a bit about what is being backed up and why.

The Basics

A backup is a safety copy of your computer’s data. It can be as specific as a duplicate of a single file or as comprehensive as everything on your computer’s mass storage system.

Backups are created by using backup software, which often comes as a utility or software tool included with the computer’s operating system.

The Reason for Backup

There are two reasons for backing up your computer’s data, a hardware reason and a software reason.

The hardware reason is that hard drives (and other mass storage media) often fail. When that hardware fails, all your stuff — documents, pictures, video, music, programs, settings, everything — is gone. When you have a safety or backup copy, you can get that stuff back.

The software reason is that programs and humans screw up. While deleted files can be recovered, changed files cannot. Lost files may never be found. When you have a backup, however, missing or deleted or lost files can be recovered from the safety copy.

Backup Strategy

To make the backup work, two things must happen:

The backup must be stored on separate media. It’s not a backup when you merely duplicate information on a hard drive elsewhere on that same hard drive. The files must be copied to another storage device, preferably something external or removable: an external hard drive, tape backup, optical discs, or a backup service on the Internet.

The backup must be done with some frequency. The older the backup copy the more irrelevant and useless it becomes. Serious users backup daily. Casual users backup weekly. The more often you backup, the more useful that safety copy becomes in times of woe.

The Process

It would be silly to just continuously duplicate all the information from your computer’s storage system. Such process would be time-consuming and inefficient. After all, the great bulk of the files stored on your computer never change.

The approach to backing up works like this:

1. Initially create a full backup, a copy of all the information on your computer. That backup includes the operating system, all programs, all your files, all settings, everything.
2. After that initial backup, only backup those files that have changed since the last backup. That would include any files you’ve added, new programs installed, plus files that you’ve modified or updated.
3. Repeat Step 2 frequently.

The end result of this process is that your backup has a copy of everything on the computer.

The backup software manages the backups you make. So when you need to restore a single file or folder, it knows how to fetch the most current version, or perhaps even an older version.

When you need to restore the entire system, then the backup software can pull together a current image using the backed up files, dates, and other information it has.

Next time: More backup strategy and terminology.