IC memory can roughly be divided into two categories. The first is Random Access Memory (RAM) and the second is Read-Only Memory (ROM). RAM can be read and written anytime but the memory will be erased once the power supply turns off. On the other hand, ROM is written slower than RAM, or it cannot be written at all. In addition, ROM can maintain its memory even if the power supply turns off. Therefore ROM is useful for read only solutions where the memory does not always have access to power.