One of the reasons why DOS For Dummies sold so well is that the operating system excelled at making you feel stupid. Case in point: It was cinchy to reformat the PC’s hard drive and lots of people did it all the time.

Today, the thought of zapping a computer’s hard drive — or “mass storage device” — is terrifying. It didn’t mean as much back in the day, probably because people assumed the entire concept of computing was magical and finding a file you created yesterday was one notch below miraculous.

Historically, most of the formatting disasters were prior to DOS version 3.2 (I believe). At the time, floppy diskettes ruled the office. The hard drive was just a convenient place to store DOS and your programs. Your data resided on removable floppy diskettes, which was mostly out of habit and not because the hard drive was slow or lack storage space.

As was common in the day, you’d reach into your disk caddy for a floppy, stick it in the PC’s floppy drive, close the latch, then use the programs on the hard drive to work with files stored on the floppy. When you were done, you’d remove the floppy and repeat the cycle.

Diskettes came unformatted. That’s because several computer systems were popular and each used its own format. A DOS computer had one format, the Apple II another, ditto for the Mac, Commodore 64, and others.

When you first inserted a diskette, you formatted it. The command was (and still is):

FORMAT

Before hard drives, you’d type that command, remove the current floppy, insert the new floppy, and press the Enter key to begin formatting. Hundreds of thousands of PC users were trained this way. Their actions were automatic.

The problem was that the FORMAT command assumed the current storage unit, such as Floppy Drive A or, when you had a hard drive, Hard Drive C. So, the user types FORMAT, inserts the new floppy, presses Enter, and the FORMAT command proceeds to format the current drive, C — the hard drive. No warnings. No errors. And when it’s done, DOS and all your applications were gone bye-bye.

Eventually, Microsoft added some safeguards to the FORMAT command. Even then, people continued to format hard drives wantonly, still out of habit. An UNFORMAT command was eventually added to DOS to address this situation.

Today, respect for the PC’s mass storage device is at an all-time high. You’d probably blanch at the thought of accidentally formatting a hard drive. But thanks to the sacrifices of your proto-computer ancestors, the odds are really low.