Some people are masters of this item, while others are – willingly or unwillingly – its slaves. With a little bit of dust, we can see its inner workings laid bare. What oh what could it be?
Try a credit card covered with magnetised rust particles.
First of all, you will notice that Gilbert’s card has three horizontal magnetic bands. This is the standard for all swipe cards. In most cases, information is recorded on one, or sometimes two of these bands. The two outside bands are called high density tracks and contain data at 210 bits per inch. If you know anything about computers, you will realise that the term ‘high density’ here is relative: 210 bits per inch, by modern data standards, is pretty damn lousy. To give you some idea, one of these tracks can carry about 79 x 6bit alphanumeric characters. Your credit card would typically have, on track 1, your name, your card number and an expiry date