There are two basic types of chip card in credit card format: Those with a processor and those without. Memory chip cards have just a simple EEPROM (electrical erasable and programmable read-only memory) of type 24Cxx fitted beneath the eight contact pads. The memory size can be from 128 Byte (1 Kbit) to 2048 Byte (16 Kbit). Control of the memory is via a two-wire interface which could be either I2C or Two-Wire-Interface (TWI) depending on the card manufacturer.