What is the Black Strip on ATM and Credit Cards?

To withdraw money from an ATM, you must insert the card correctly into the machine's slot. The card is recognized only if the black strip on it faces the required direction. Many electronic cards have this black strip, which is called a magnetic strip.
A magnetic strip is a thin film made by mixing fine particles of magnetic metal (like iron) into plastic. When iron particles come close to a powerful magnet, they become magnets themselves, and the particles align in a row. A magnetic recorder, similar to what is found in a tape recorder, tapes the cardholder’s details, card number, etc., onto this strip.
When the card is inserted into the machine's slot, this magnetic strip faces the card reader. The card reader contains a wire coil. Due to the magnetic field, an electric current is generated in the coil. This current goes into the computer circuit, and the card details are decrypted. The data on the strip is marked with vertical lines, much like a barcode. These microscopic lines belong to the magnetic field and are not visible to us.
The data on the magnetic strip of an ATM or credit card remains preserved for years. However, care is necessary. It should not be kept near powerful magnets or allowed to become excessively hot. Doing so weakens its magnetic field and erases the data.