Magnetic Stripe Technology

A magnetic stripe is the band of magnetic material on the back of credit, debit, identity and access cards used to store a small amount of machine-readable data. The stripe is made of tiny magnetic particles held in a film, much like the coating on magnetic recording tape. Information is recorded by magnetising regions of the stripe in particular directions; a card reader detects the pattern of magnetisation as the card is swiped past a read head and converts it back into data.

Standard cards carry the data on parallel tracks running along the stripe, and international standards define how these tracks are laid out and what they contain. The data is stored using a self-clocking scheme commonly called two-frequency, or F2F, encoding, in which the spacing of magnetic flux reversals distinguishes a binary one from a zero. Because the timing reference is built into the recorded pattern, the reader can recover the data reliably even when the card is swiped at an uneven speed by hand.

Magnetic stripes are inexpensive and were long the dominant technology for payment and identification cards, but they have limitations. The stored data is static and fairly easy to copy, and the stripe can be damaged or erased by physical wear or strong magnetic fields. These weaknesses have driven a shift toward chip cards and contactless technologies that perform cryptographic operations, although magnetic stripes remain in wide use, often alongside a chip on the same card for compatibility.

Frequently asked questions

How is data stored on a magnetic stripe?

Regions of magnetic particles in the stripe are magnetised in specific directions. A reader senses this pattern of flux reversals as the card is swiped and decodes it into data.

Why are magnetic stripes being replaced?

The data is static and easy to copy, and the stripe wears out or can be erased. Chip and contactless cards add cryptographic security that a plain stripe cannot provide.

Why can a card be swiped at any speed?

The encoding is self-clocking, embedding its timing reference in the recorded flux pattern, so the reader recovers the data correctly even at an uneven swipe speed.