Magnetic stripe

It was invented at IBM in the 1960s. The legend goes that engineer Forrest Parry could not get any glue to hold the stripe until his wife suggested pressing it on with an ordinary clothes iron. The band carries up to three tracks: tracks 1 and 2 hold the card number and expiry, in formats set by the airlines' IATA and the banks' ABA, and standardised in ISO/IEC 7811.

A swipe reader senses the flux reversals as the stripe passes the read head — the same basic principle as magnetic tape, only on a centimetre of plastic. The technology is on its way out: EMV chips and contactless replace it because a stripe is trivial to clone, while the cousin that reads printed digits magnetically, MICR, lives on across the bottom of cheques.