a method for modification of data in a card transaction system having a memory card and a reader for reading the card . the card has a first memory and a second memory with data locations occupied by data recordings . each transaction involves the modification of at least one of the data locations or the addition of a new recording . the method reads the address of a free location from a previous control register located in a first fixed location in the eeprom memory , writes the new modified recording or addition in the free location , repeat the steps for each new recording to be modified or added , and writes in a second fixed location in the eeprom memory a new control register containing the addresses of free locations within the eeprom memory to use in the next transaction .