How are cards with magnetic stripes decoded?

Cards with magnetic stripes are read by swiping the card through a device containing a tiny coil of wire. The movement of the magnetized spots over the coil causes small electrical voltages to appear in the coil and from these voltages, the stored binary data is decoded. The reader then sends the decoded data to a PC via a USB, parallel port, or serial port cable. There are many low-cost magnetic card readers available in the market today.