As you probably already know, your debit card is more than a flexible piece of plastic. The dark strip on the back of the card actually holds all of the financial data that is associated with that card! But how in the world does that strip serve as a data storage device? Read on to find out...
The Mechanical Principle of Data Storage
With the discovery of the binary code (everything described as yes/no, or 1/0), came punchcards in the 1950s. They were largely used in banks and financial institutes. Up to 80 characters, called bits, could be "saved" on one such cardboard card. The information was saved by punching in holes for yes and leaving the card intact for a no. The resulting information could be read out mechanically.
NOTE: For more on binary code see "Jamming to Your Favourite Tunes: Decompressing the Meaning of MP3s"
The Magnetic Principle of Data Storage
A more modern technique to store data is to use the different orientations of small regions in magnetic materials. This method is used for most modern hard discs, only with newer materials and components. The dark data storage strip on your debit card is also made up of magnetic materials.
Specific orientation of the small magnet particles within a solid determines whether the state denotes "yes" or "no", "1" or "0". Read/write heads in hard discs and audiotape players can write and read that information onto the magnetic material of the data storage device.
Did you know? Examples of magnetic data storage devices include floppy disks (you know...those 3"x3" discs that almost no one uses any more), hard discs, audio cassette tapes, debit cards, and credit cards.
The first magnetic data storage media were toroidal core memory rings, first built in 1958. These were quite bulky and every bit (0 or 1) was visible to the naked eye. When the information was read out, the data was overwritten with a 0 and thus, immediately after reading, the data had to be rewritten to the same core in order to not be lost. Not very efficient, huh?
Today's technology varies significantly as reading no longer destroys the data. There are permanent magnets like hard discs. Temporary magnets like computer memory chips require a permanent source of energy, usually an electric charge, about ten times per second so as not to "forget" the stored data due to de-alignment of the magnetic particles.
Other applications of the magnetic storage device include forgery-proof bank cards based on something scientists have dubbed the GMR-effect (Giant Magnetic Resistance). This is an effect happening in very thin (few nm) layers of special metallic alloys are applied on the magnetic strips of bank cards. This layer could be coded during creation and is, supposedly, not forgeable — until someone discovers how to change that coding in the future...
Can you figure out why you should not put your debit card too close to a magnet? The magnet will attract or repel the materials in the magnetic strip, causing the small regions to realign.
This, in a nutshell, will "erase" or at least alter any data that is encoded on that magnetic strip. The card is then useless and will have to be replaced. However, you will not be able to hide the purchases you made over the holiday season; even if you erase the data from your debit card, your bank will still have a record of your shopping history.
Lars Rose is a PhD candidate in high temperature Solid Oxide Fuel Cell research (that is sustainable energies), at the Department of Materials Engineering in the Faculty of Applied Science at the University of British Columbia (UBC), and at the National Research Council Canada, Institute for Fuel Cell Innovation (NRC-IFCI). He enjoys teaching fun stuff and is the current Media Relations and Human Resources coordinator of the outreach program Let's Talk Science at UBC. He enjoys writing science in a fun way for CurioCity, UBC Terry, the Science Creative Quarterly, Fuel Cell Today and Ubyssey.